Actors' Equity Association, the union for professional stage actors and stage managers.
When a production is described as "Equity", its actors and stage managers are union members working under a professional contract. "Non-Equity" productions, including most community theater and many tours, are not under that contract. Neither label tells you how good a show is; plenty of wonderful nights happen on both sides of the line.
Also seen as: Actors Equity, Equity actors, Equity contract, non-Equity, Equity production