Wow, I thought you knew everything .
I guess it has something to do with bits (duh, it's reading from a stream) and maybe variable.
It'd be a logical word choice.
What it's exactly being used for I do not know.
I did notice it's being used in EntityDefinition and ObjectDefinition, and with something about animable and interfaceValues.
If you know more, please tell me.
I'm learning, refactoring and attempting to understand the client, so this would be a great leap forward.