A flat-screen television, or more accurately a flat-panel television, is a television set with a thickness usually under 10 cm (~4 in.). This is opposed to cathode-ray tube televisions or rear-projection televisions whose designs required rather thick housing.
This tag is specifically for flat-panel tvs, which the term "flat-screen tv" is used interchangeably with today. It should not be used for rear-projection tvs or flat-screen cathode-ray tube tvs, which were particularly common before LCD and similar technologies become the dominate technology used for televisions.