What does 'ten of six' mean in regard to time?
In a Family Guy episode (The Hand That Rocks The Wheelchair), Meg asks "is it 10 of 8?", apparently looking up at the clock and referring to the fact that the time is 7:50. Is this a commonly used term to refer to the time as being "10 minutes to 8", or is it just a Family Guy thing? If it's common (I've never heard it before), what does it stand for, if "10 to 8" stands for "10 minutes to 8"?