A more thorough explanation:

A State Bar Association is a group of lawyers who have been admitted to practice law in a particular state. It is usually created by statute and membership is often mandatory for those who practice law in the state. Unlike voluntary, professional-development bar associations such as the American Bar Association, state bar associations often have the authority to regulate the legal profession, by undertaking such matters as disciplining attorneys and bringing lawsuits against those who engage in the unauthorized practice of law.

• Several state bar associations sponsor superb CLE programs.
• The California State Bar Association is responsible for regulating the legal profession in California.
• Membership in the New York State Bar Association is mandatory for all lawyers who practice law in New York.

The examples illustrate that state bar associations are organizations of lawyers who are admitted to practice law in a particular state. They are responsible for regulating the legal profession in that state and often have the authority to discipline attorneys and bring lawsuits against those who engage in the unauthorized practice of law. Membership in state bar associations is often mandatory for lawyers who practice law in that state.