Bitrate describes the rate at which bits are transferred from one point to another. In simple language, it measures how much data is transmitted from one point to another in a given amount of time. Commonly, bitrate is measured in megabits per second (Mbps), kilobits per second (Kbps) or bits per second (bps).
Bitrate can describe the quality of an audio or video file. For instance, a video file that is compressed at 4000 Kbps will look much better compared to the same file that is compressed at 2000 Kbps. The quality of a video or audio file is measured by the bitrate just like the quality of an image is measured in resolution.