Something that intercepts. Seriously, this term is typically used to refer to a warplane designed to intercept (and destroy) incoming threats - an air defense fighter. Typically, the incoming threat is a bomber or cruise missile.

The film Mad Max pictured a dystopic future Australia where the highway police employed special cars and drivers to deal with high-speed felons. These were called Interceptors.

Aircraft so designated are typically quite fast and emphasize air-to-air armaments. Their speed allows them to engage enemy threats as far out from their targets as possible.