Within the industry, a lot of terms can be bandied around with little to no context or definition surrounding them. Hopefully this A-Z list of definitions can set you straight and hlp build your plant care knowledge. 

A

Abaxial (Surface): Refers to the underside of the leaf, or the lower surface. Facing away from the sunlight.

Adaxial (Surface): Refers to the upper surface of the leaf. Facing towards from the sunlight.

Aerial: Growing above the surface of the ground or water            

Alkaline: Basic especially, of a soil or solution : having a pH of more than 7            

Annual: A plant that completes it's life cycle within a single year or growing season          

Apex: The branch or stem tip; the furthest point from ground level or point of soil attachment

Aphid: Small sap sucking insects, usually green, black or yellow in colour; Aphidoidea      

Apical: Located at the apex of a structure, usually refers to new shoots, stems or the trunk of a tree

Arborescent: Tree-like growth or general appearance            

Asymmetrical: Irregular or unequal; lacking any plane of symmetry; e.g. flowers of Canna             

Axil: The upper angle between one part of a plant and another, e.g. the stem and a leaf 

Axillary: Arising from the axil, usually referring to the axil of a leaf

B

Bark: Protective external layer of tissue on the stems and roots of woody trees and shrubs           

Basal: Situated or attached at the base 

Biennial: A plant which completes its life cycle within two years or growing seasons         

Bifoliate: Having precisely two leaflets, usually in a symmetrical pair        

Bulb: A thick storage organ, consisting of a stem and leaf bases 

Bulbil: A bulb arising from another bulb

Bright (Sunlight): Refers to sunlight that is directly shining through a window in your home sometimes referred to as direct sunlight  

C

Canopy: The raised foliage of a tree or tree like plant, also referred to as the crown                          

Callus: Soft tissue that forms over wounding, arising from within the stems. Disorganized cell growth.

Cataphyll: Any tissue formed by the plant which carry or transport the leaf out of it's growth point, these usually shed once they have completed their main function  

Caudex: woody stems which store nutrients at the basal area of a plant usually bulbous and growing above the soil                               

Chlorophyll: Chemical pigments contained within the chloroplasts that are essential for photosynthesis                 

Chloroplast: An organelle existing in plant cells which contain chlorophyll                             

Chlorosis: Abnormal or pale colouration observed in plant organs which are normally green         

Climber: A plant growing upright with the assistance of another structure either clinging with tendrils, roots or twining around it                             

Coir: Fibrous husk from the outer shell of a coconut, used for potting plants, totem poles and compost                   

Cotelydon: The first leaf or leaves to emerge from a seed generates energy to produce the plants first leaf or set of leaves                  

Cultivated: The practice of looking after or raising plants, either from seed or cutting                       

Cultivar: Originating from "cultivated variety" refers to a group of plants showing the same characteristics, reproduction or cloning of these plants produces the same variant. Usually the result of hybridisation or stable mutation                            

Cutting: Used for propagation or asexual reproduction, normally refers to apical tip of plant structure, root or leaf

D - E

Deciduous: Refers to the falling of bark leaves or petals seasonally. Usually during winter

Dicotyledon: Commonly known as Dicot, a flowering plant which has two or more cotyledons

Dripline: An area located directly under the canopy of arborescent plants, the outer circumference of a trees branches.

Eae: A suffix placed at the end of genus' name to form the name of a tribe or family

Endemic: Plants which occur natural and are restricted to a certain geographic region

Epilithic: Organisms which grow on stones or rocky surface

Epiphyte: A plant, algae or fungus which grows upon another organism for support and not nutrients

Evergreen: Not deciduous; displaying foliage all year round

F - G

Family: A category referring to one or more genus' sharing physical or historical similarities

Fenestrate: Having holes or translucent areas, noticeable in mature monstera leaves

Frond: The leaves of cycads, palms, and ferns

Gall: External growth formed on plant tissues, usually noticed as swollen stems caused by various parasites, fungi, and bacteria; Gall wasp on citrus trees

Genus: A grouping of species with historical and/or physical similarities. Refers to the first name in botanical Latin i.e. Monstera

Germination: Describes the changes which occur as seeds begin their growth stage

Graft: The artificial or manmade interference which joins two plant parts to grow together

Groundcover: Densely growing plants which smother the soils surface

Guttation: Description of plants releasing excess moisture through sharp points toward the end of leaves

H - I

Habitat: The place a plant lives; environmental conditions of its natural home

Habit: The standard look of a plant; shape, size, texture, and orientation

Hardwood: Dormant cuttings taken from trees or plants which lose their leaves in winter; deciduous

Herbaceous: Vascular plants which at no point in their life cycle produce a woody stem

Herbarium: A preserved collection of plant material, inclusive of seeds, leaves, stems and flowers

Hybrid: Plants which have been produced using parents from two separate groups, genus or species etc.

Hydrophobic (Soil): Soil particles which have become dry and coated with an oil based film, unable to absorb moisture

Hyphae: Filaments described to make up fungus tissue, commonly seen connected to plant root hairs, a product of mycorrhizal symbiosis

Indirect (Sunlight): Light which illuminates but does not directly shine upon a surface

Inflorescence: Term used to describe flowers which form closely together in an efficient unit

Internode: Stem sections located between two nodes

J - M

Juvenile (Leaves): Leaves produced by younger plants, normally differ from mature specimens   

Lithophytic: Plants that grow on rocks   

Loam (Soil): Loose sandy soil, with a higher percentage of silt as opposed to thick water retaining clay soils

Mealy Bug: White waxy sap sucking insects, found under leaves and in plant crevices      

Meristem: Actively growing plant tissue which divides   

Monocotyledon: Flowering plants which produce a singular cotyledon; Monocot              

Mutation: Similar to humans and animals, mutation refers to genetic characteristics of plant species through growth habit or colouration       

Mycorrhiza: Symbiotic relationship shared between the roots of plants and fungus          

N - O

Native: Plants which naturally grow in certain areas but are not confined to them             

Nectary (Extrafloral): Glands in plant tissue which secrete nectar similar to a flower, can cause brown spotting on some plant species where the sun burns these sections 

Node: The stem section which leaves or branches grow from      

Noxious: Plants with harmful or unpleasant qualities, used to refer to unwanted weeds that can harm the native environment    

Offsets: Young plantlets which grow around the base of certain plant rhizomes  

P - Q

Palmate: Leaf that has veins radiating outward from a certain point         

Peat (Moss): Fine dry moss used for propagation and soil mix, harvested from bogs. Usually high in acidity

Peduncle: The stalk that holds up inflorescence

Perennial: A plant which survives longer than two or more life cycles      

Perlite: A volcanic glass aggregate, light and good for insulation or plant media  

Petiole: The stalk connecting a plants leaf to the main stem         

Phloem: Channelling tissues which transport sucrose throughout the plants body              

Photosynthesis: A process which mostly all plants are capable of, converting water and carbon dioxide into simple sugars  

Pup: Similar to offsets refers to young plants grown from a main rhizome or stem

R

Radicle: The first or central root formed out of the seed embryo

Rhizome: A long lived stem which grows underground, horizontally. Resembling a swollen root

Root: Plant tissue which grows underground, usually downward or horizontally. Absorbing nutrients and for support

Rooting (Hormone): Powder or gel used to promote the growth of new roots, full of nutrients and hormones for plant growth

Root Hairs: Outermost cell growths protruding from root tips, function as water absorbing organs

Rootstock: Specifically selected plants grown for their roots alone, to be grafted upon

Runner: Slender stems underground which grow horizontally producing new roots and shoots, commonly seen in grasses

S

Seed: A ripened propagating organ with a protective coating covering the plant embryo

Self-Heading: Plants which grow similarly to a tree, technically still vines but with a much more upright growth habit and thick stem

Shoot: Aerial portion of a plant, inclusive of stems and all it's important organs

Sinus: The top section of the leaf where the petiole meets leaf tissue, usually concave.

Spadix: A spike like inflorescence crowded solidly around a stout

Spathe: The large leaf like covering surrounding a plants inflorescence

Species: The classification specifying a certain plant, the second name in botanical Latin; Monstera "deliciosa"

Sphagnum (Moss): Thick dry moss used for propagation, harvested from bogs. Usually high in acidity

Spider Mite: Small sap sucking mites which spin webs where the petiole joins the leaf

Spore: A propagation particle produced by mushrooms and ferns

Sport: Random variation occuring in natural plants, plants mutating to differ from their parent plant

Stem: The plants major organ bearing nodes, leaves flowers and branches

Stolon: Slender stems underground which grow horizontally producing new roots and shoots, commonly seen in grasses

Stoma: Small pore like holes found on the leaf surface, allowing the absorbtion of gases and nutrients through the air and water

Substrate: Refers to the surface matter which an organism lives and grows

Succulent: Plants with thick fleshy habit which can store water within their foliage

Sucker: Shoots originating from the basal area, roots or Rhizome of a plant

T - U

Taproot: Similar to radicle root, it defines the plants root system as one dominant root

Tendril: Modified slender stems climbing plants use to attach themselves to an object

Terrestrial: Growing on, or along the ground

Thrips: Tiny Sap sucking flies, shapes like a grain of rice the larvae start as creamy transparent bugs and the adults are slightly bigger black flies

Tuber: Term used to define a variety of the underground vegetative storage organs

Transpiration: The process where plants take up water from the soil and it travels through their body until evaporating from the leaves through pores called stoma

Understory: Plant life growing underneath tree canopy, thriving under indirect light

Uproot (Uprooting): This refers to a process where you pull plants out of their pots or out of the ground, revealing their roots

V - X

Variegated: Irregular marks or patches of unnatural colour within a plant              

Vein: Tissues within the plant conducting the transport of waters and sugars       

Venation: The way in which veins are arranged within a leaf        

Vine: Plants which climb or trail by means of support from tendrils or runners    

Weed: Any plants which are found to grow where they are unwanted or disrupting habitat           

Xylem: Similar to phloem, tissues which transport water throughout the plant