Definition of "SSR"

(historical) Initialism of Soviet Socialist Republic.

(aviation) Initialism of secondary surveillance radar.  examples

(electronics) Initialism of solid-state relay.  examples

(US, military, nautical, obsolete) Initialism of Sub Surface Radar — a radar picket submarine.

(aviation, travel industry) Initialism of special service requirement (or Request).  examples

(statistics) Initialism of sum of squared residuals.  examples

(web development) Initialism of server-side rendering.  examples

(education) Initialism of sustained silent reading.  examples

(nautical) Initialism of Small Ships Register.  examples

(military) Initialism of Special Support and Reconnaissance.