Crown Thin: selective removal of branches throughout the canopy to minimize the risk of limb failure, by decreasing tip weight and reducing wind drag. The focus of crown thinning is on the outer tips of the branch.
Crown Clean: removal of any dead, dying, and diseased branches. Also includes the removal of any crossing or rubbing limbs throughout the tree.
Crown Raise: raising of the bottom canopy to a specified height above the ground. Sometimes for aesthetics and sometimes for specified height above sidewalks and streets dictated by city code.
Structure Prune: pruning back of competing leaders in a tree to encourage a strong central leader. Usually done on younger to mid-size trees to train them for better structure as larger mature trees.
Selective Prune: pruning of a specific part of the tree discussed by homeowner and arborist. This can range from thinning over a structure to complete removal of limbs for house or yard clearance.