Professional theater using career & union arts personnel. A full-time administrative staff is in place, at least 90% of mainstage productions use union cast, directors, crew, etc. Non-union personnel are paid. These companies may have alternate, small black-box productions that use non-union or unpaid personnel, but their main, bread-n-butter productions pay living wages.
Professional theater using a mixture of career and part-time arts personnel. At least some administrative staff are full-time. At least 90% of mainstage productions use paid personnel, though not necessarily at union rates (or "living wages"). A few union personnel may be used, but this is not the norm.
Non-professional theater using part-time, unpaid arts personnel. May have the mission to provide artistic outlets to community members, or may be a start-up theater with aims at becoming professional. There may be one or two full-time paid administrative staff and small stipends for key artistic personnel (e.g., director), but the vast majority of personnel receive no wages.
Educational institution. High school, college or university. Also includes private acting schools.