ATSC (short for Advanced Television Systems Committee) is a large consortium (constituted by ~140 members from the broadcast, broadcast equipment, motion picture, consumer electronics, computer, cable, satellite, and semiconductor industries) that develops a set of standards related to Digital TV.
In particular, the ATSC developed, and self titled, "ATSC Digital Television (DTV) Standard (A/53)", along with several other associative ATSC standards, have been adopted by the U.S.A, Canada, Mexico, South Korea, and perhaps some other countries, for terrestrial based over-the-air (OTA) digital television broadcasts. In casual conversation or less precise descriptions, the terms "ATSC" or "ATSC Standard" are used generically to shorten the reference to such systems.
Similar to other DTV systems, the A/53 and helper standards call for the transmission of a MPEG-2 Transport Stream, but in regards to its modulation onto an RF carrier wave, the 8VSB modulation scheme is used instead of COFDM, as employed by the competing DVB-T counterpart. During the DTV trial stages, and as well as for near close to a decade following the 1996 U.S selection of the ATSC DTV Standard for use in terrestrial transmissions, a kind of holy war has been waged in some circles as to whether which of DVB-T or ATSC is the technically more advanced system. For one such analysis of these two systems, see here. In 2001, a report compiled by the COFDM Technical Group concluded that COFDM did not offer any significant advantages over 8VSB. Much of this debate has subsided over the course of time.