The number of bits in each audio sample. The higher the bit rate, the larger the potential dynamic range of the sound.
For example, a 16-bit sample size provides much more dynamic range than an 8-bit sample size. Choose 16-bit for music that has both soft and loud sections, such as orchestral music. For spoken voice or music that has a more or less constant volume level, choosing 8-bit sound can still yield good results and will result in a smaller file size.
If you need to shrink your media file, you can reduce the sample size from 16 bits to 8 bits. This cuts the file size in half but also degrades the audio quality.