Yep, like sercero says, look at it as the cache or buffer for running programs. It is dynamic and always changing depending on what's loaded and running. It's not very big but it's the nature of the beast as they say.
Your other memory is simply where you can store things like video, music, data, apk files etc.
People have tweaked things and the most I've ever seen available is ~96mb. Seems GB leaves less available than 2.1. This is something tipstir is constantly trying to get the max amount available through his mods.