Initialism of standing room only.

• Label on tickets, signage, or listings when seats are sold out.

Initialism of senior-ranking officer.

• The highest- or senior-most officer present.

Initialism of school resource officer.

• A sworn police officer assigned to a school.

Initialism of single-room occupancy.

• A small rental unit with shared kitchen or bathroom.

Initialism of self-regulatory organization.

• An industry body that sets and enforces member rules.