A baby conceived from having sex in a car, usually, but not limited to, the backseat.
Because Ricky and Charlotte have only had sex once, in the back-seat of his car, and she is now pregnant, her child would be considered a Back-Seat Baby.
by Charlotte Lyons March 21, 2009
Term meaning WHORE when there are seven year olds in the room.
"You don't want your identity to be the biggest back seat baby in the school."
by VapoRub Baby April 29, 2006