See data rate
The speed that digital audio and video files are encoded (compressed), measured in kilobits (Kb) and megabits (Mb) per second. For example, MP3 audio files can be created with bit rates from 16 Kbps to 320 Kbps, with 128 Kbps being fairly common. Video formats also run the gamut, from as little as 10 Mbps for preview frames to 400 Mbps and higher for HD.
The higher the bit rate, the less compression and the better the audio or video quality. It is sometimes extremely difficult to hear or see the difference unless comparing content with bit rates that are far apart. See space/time