Nitty gritty
Nitty gritty is a colloquial term for the real thing, the actual raw reality of the situation.
Etymology
According to the Oxford English Dictionary Online, the term started as US slang but its origin is unknown.
One theory is that it was first used to refer to the slaves on the lower levels of a ship and is a politically incorrect expression. However the first recorded written use of the phrase was in 1956 and it would be very unusual for a phrase to exist in the vernacular for more than 100 years without it being recorded.