There are several specific types of pruning that help trees stay healthy, safe and beautiful.
Cleaning removes dead, dying, disease, crowded, weakly attached and low-vigor branches from the crown of a tree.
Thinning is the selective removal of branches to increase light and air movement through the crown. Thinning also reduces weight on heavy limbs to maintain the natural shape of the tree.
Raising removes lower branches from a tree to clear space for buildings, vehicles, pedestrians and views.
Reduction trims the height or spread of a tree by pruning back the leaders and branch terminals to lateral branches that are large enough to assume the terminal roles (at least one-third the diameter of the cut stem). Reduction helps maintain the form and structural integrity of the tree.