Bitcoin users on reddit and bitcointalk have declared June 2 as “M Day.” They want everyone to start using mBTC whenever possible in place of identifying prices as whole bitcoin. mBTC is 1/1000th of a BTC. When an item is 0.01 BTC, it’s easier for many to read it as 10 mBTC. This should help lead to wider adoption of bitcoin as a whole.
So far, I haven’t found an agreed-upon way to pronounce it. So far, I’ve heard bitcent, millibit, and mbit. Personally, I vote mbit.
zinodaur made this graphic to illustrate: