A capitalization error, the difference between "Help your Uncle Jack off a horse" and "help your uncle jack off a horse"
Cowboy 1: Hey, partner! Go help your uncle jack off a horse!
Cowboy 2: How many times do I have to tell you, it's "help your Uncle Jack off a horse!
Cowboy 1: Oh, sorry for making that homosexual grammar error!
A really cool-looking house; a large house, mansion
The origin comes from the nursury rhyme "The house that Jack built" It is unsure who "Jack" really is, but it is believed that he may have been Jesus, since Jesus was a carpenter.
Man! I knew that Bill Gatesguy was rich, but have you seen his house? THAT is the house that Jack built!