aa - yes it really is a word.

[Jet Cash]

aa is the first entry in the Oxford English Dictionary, and it refers to a type of volcanic rock. If you are a reader of the Fit to Talk English project for Bitcoin Talk members who don't have English as a first language, you would be able to discover information like this. We try to make learning and improving your English fun, but we still need help in our mission to improve posting in the Bitcoin Talk forum.