For regulations surrounding bit rate, see: Ranking criteria
For help re-encoding audio to a different bit rate, see: Audio editing guide.
Bit rate is a measurement of data throughput for a media file in units of bits over time. In osu!, this is relevant when talking about the quality of audio files: higher quality audio typically requires a higher bit rate, while lower quality audio can use a lower bit rate.
Bit rates of audio files typically range from 96kbps (kilobits per second) to 320kbps. The ranking criteria require that song audio is in the 128–192kbps range, and AiMod will warn if this is not the case.