ATSC

An ATSC tuner (also referred to as an ATSC receiver) allows reception and decoding of ATSC digital television (DTV) signals broadcast over the air by television stations. ATSC tuners perform a number of tasks to fit the television signal received to the particular television display including:
Demodulation: signal is transformed into a usable signal for image display and sound.
Transport Stream Demultiplexing: separation of multiple digital signals broadcast at once (multiplexing)
Decompression: compressed digital signals are restored to their original size
Error Correction: used to ensure any missing data due to factors such as interference or poor signal reception is corrected if possible
AV Synchronization: accurate synchronization of audio and video signals
Media Reformatting: to suit format of television set which may be interlaced or progressive

QAM or Clear-QAM Tuner

A QAM (Quadrature Amplitude Modulation) tuner enables the direct reception of un-encoded (in-the-clear) digital cable channels without a set-top box. QAM is the format utilized by digital cable channels to encode and transmit their content. There is no FCC requirement that QAM tuners be included in new televisions.

CableCARD

A CableCARD is a plug-in card supplied by a cable company to allow viewing and recording of digital cable television channels without the use of other equipment such as a set-top box. A CableCARD is not in fact a receiver but, performs the identification and authorization of the customer and decodes the digital cable signal.