TSP is abbreviation established by International Civil Aviation Organization - ICAO to adress specifically authorized organization for purpose of language proficiency assessments of flight crew and air traffic controllers.
TSP stands for Testing Service Provider and the name was established in ICAO Doc 9835. Testing Service Provider or TSP has its own structure and management systems. For the purpose of language proficiency assesments, it refers to ICAO English language proficiency Testing Service Provider.
Testing Service Provider must be in possession of holding own Operation manual and Quality management system. Testing Service Provider (TSP) is certified by an ICAO member state's National Aviation Authority.
In EASA region, the equivalent of Testing Service Provider is called LTB or Language Testing Body.