The term 'Is this thing on?' is a phrase often used to check if a microphone or other audio device is working. The crossword solutions for this term are TEST (4 letters) and TAP (3 letters). TEST is an acronym for Transmitter-Emission-Signal-TEST, which is a procedure used to check the performance of a radio transmitter. TAP is an acronym for TEST Access Point, which is a device used to TEST the performance of a network.