The bitrate represents the quality level of the mp3 compression. A higher bitrate means better quality, but adds weight to the mp3 file. The bitrate you use when compressing your mp3 files depends on your needs, here are some of the common bitrates and their quality levels.
16 kbit/s - Minimum (Ideal for voice/speech)
32 kbit/s - Intermediate
64-96 kbit/s - Recommended
128 - 256 kbit/s - CD Quality