The American national Standard for tree pruning is ANSI A300.

Its development process was approved by the American Standards Institute

The A300 standard has been drafted to address pruning specifications across all geographic areas. Knowledge of the growth habits of certain tree species within a given environment may alter how the recommendations of A300 are interpreted.
With the American National Standard for pruning, ANSI A300, specifications can be written in a virtual infinite number of combinations The following information is designed to help you understand exactly what will be accomplished in a pruning operation.

Branch Size - A minimum or maximum diameter size of branches to be removed should be specified in all pruning operations. This established how much pruning it to be done.

Pruning Objectives
Hazard Reduction Pruning (HRP) - Is recommended when the primary objective is to reduce the danger to a specific target caused by visibly defined hazards in a tree. For example, HRP may be the primary objective if a tree has many dead limbs over a park bench.

Maintenance Pruning (MP) - Is recommended when the primary objective is to maintain or improve tree health and structure, and includes hazard reduction pruning. An example here might be to perform an MP operation on a front yard tree.

Pruning Types
Hazard reduction pruning and maintenance pruning should consist of one or more of the pruning types noted below:

Crown cleaning - The selective removal of one or more of the following items: dead, dying or diseased branches, weak branches and watersprouts

Crown thinning - The selective removal of branches to increase light penetration, air movement and to reduce weight

Crown raising - The removal of the lower branches to provide clearance

Crown reduction or shaping Decrease the height and/or spread of a tree. Consideration should be given to the ability of the species to sustain this type of pruning

Vista pruning - The selective thinning of framework limbs or specific areas of the crown to allow a view of an object from predetermined spot

Crown restoration - Should improve the structure, form and appearance of trees which have been severely headed, vandalized or storm damaged.