“A.B.A.” is an abbreviation that can mean several things depending on context:

• American Bar Association — the main professional organization for lawyers and legal professionals in the United States.

Other meanings:

• Applied Behavior Analysis — a scientific approach used in psychology and therapy, especially for autism treatment.
• Associate of Business Administration — a college degree in business studies.
• American Basketball Association — a former professional basketball league (and also a modern minor league using the same name).

In short, A.B.A. most commonly refers to the American Bar Association, but it can vary by field.