Understanding the terminology of bonsai can help you from getting lost when trying to understand more advanced discussions.
Air-Layering - a technique to create roots at a new part of the tree. This is used as a propagation method and used to replace the existing root system.
Akadama - a Japanese native soil that allows roots to penetrate and grow through the particles
Apex - the highest point of a tree that can include a single branch or a small group of branches
Apical - most vigorous growth produced by a tree that is typically at the end of a branch or at the upper canopy.
Back Budding - a technique to encourage growth further back along the branch or trunk by pruning the apical growth.
Bud Break - the point at which the bud has opened enough to show a green tip.
Branches (Primary, Secondary, Tertiary) - Primary branches grow directly from the trunk; Secondary branches grow directly from the Primary branches; Tertiary branches grow directly from the Secondary branches.
Broad-leafed Evergreen - Trees with leaves that are broad that do not change color and fall off during Autumn.
Conifer - Trees with needles or scale-like foliage that are evergreen.
Bud - organ or shoot containing an embryonic branch, leaf or flower.
Cambium - green growth tissue directly below the bark; it's increase adds to the girth of roots and stems.
Callous - tissue that forms over a wound on a branch or trunk as part of the healing process.
Candle - name given to the extending bud of a Pine tree before the new needles open.
Chop - heavy pruning and height reduction of the tree trunk.
Deadwood - a special technique used to create deadwood on a Bonsai which enhances the character of and, ages the appearance of a tree.
Deciduous - broad-leaved trees which harden off and shed their leaves in the Autumn followed by dormancy during the Winter.
Defoliation - removal of all or most of a tree's leaves to reduce leaf size and vigor of growth.
Die Back - death of growth beginning at the tip due to disease or injury.
Evergreen - a plant that remains in leaf year round, slowly shedding old leaves while being replaced by new growth.
Form - the main direction in which the trunk of a tree grows.
Graft - a technique used to meld or attach a branch to the stump of a tree.
Internode - the section of growth between two nodes (leaves or leaf-joints).
Jin - removal of bark on a branch to create deadwood.
Mame - Bonsai trees less than 6"/15 cm in height.
Nebari - the flare of the roots that sometimes creates a mound.
Node - growth point on a branch or trunk from which leaves, leaf-buds and shoots can appear.
Petiole - the stalk of a leaf that attaches the leaf to the branch.
Phloem - a layer of the branch that is used to transport fluids and nutrients
Pre-Bonsai - a young tree that has not yet been trained.
Pruning - most important method in training a Bonsai by trimming leaves and/or branches.
Ramification - repeated division of branches into secondary branches by means of pruning.
Seasonal Bonsai - a species that look their best for only a short time when in flower or fruit.
Shari - technique used to create deadwood on trunk.
Shohin - name given to Bonsai less than 18"/45 cm in height.
Soil - the growing medium used for Bonsai. Typically made of mostly inorganic substrates
Sphagnum Moss - general name given to a long fibred moss used as an organic soil component for Bonsai and air-layering; has a great ability to absorb and hold moisture.
Style - the way in which a Bonsai has been shaped in order to compliment the form (direction) of the trunk.
Substrate - the growing medium in which a plant grows.
Terminal - apical; outermost tip.
Terminal Bud - a bud formed at the tip of a stem, twig or branchlet.
Trunk Leader - uppermost branch on a previously cut off trunk that is trained to grow vertically as an extension of that trunk.
Wiring - a technique using wire to bend a branch or trunk in a certain direction thus training it to grow in that way.
Xylem - area below the cambium layer in a trunk.
Yamadori - material collected from the wild.