Pilot
A pilot is the first episode of a TV series, produced as a test to gauge audience interest and determine if the show will be picked up for a full season.
Proof of Concept (POC)
POC (Proof of Concept) is a short version or sample of a film, TV show, or project used to demonstrate its viability to investors and studios.
Pilot Episode
A Pilot Episode is the first episode of a television series produced to test the concept and cast before a full series order is committed — with many produced pilots never making it to air.