ATSC stands for Advanced Television Standards Committee. An ATSC tuner is a digital tuner. To receive digital broadcasts, the television or set-top box must be equipped with an ATSC tuner.
NOTE: Not all digital signals are high definition (HD); the majority of digital signals are actually standard definition (SD). The main difference is that HD signals contain more information than SD, which translates into much more picture detail, providing a sharper, more photographic-type image.