defines the quality-to-compression
ratio of any given audio
or audiovisual file.
Theoretically, any bitrate is possible, ranging from 1 kilobit-per-second (kbps) to infinity (although one can not reach infinity, but thats another node altogether).
For example, the MP3 audio standard, used for audio recording, uses 128kbps as its mainstream standard. That means that the resulting file will be of mediocre quality and sizing about 1 MB per minute. By raising the rate of encoding, say to 192kbps, the file will grow in size, but it will be defined by better audio quality. With video files it's somewhat different since you have to add both the video and audio streams to one file, making it even larger. High compression in video files leads to fuzziness in the picture, less colors, less smoothness, etc.
The general rule of thumb is:
The higher the bitrate, the better the quality.
And vice versa of course.