Space Boomer, or often just "boomer," was a term in 22nd century Earth slang for an individual born on a space ship, and spent most or all of his or her life there. Crews of that era's Earth Cargo Service vessels were considered boomers.
The nickname persisted in somewhat diminished usage through the 2300s and well into the 24th century. Dex Oberlin, conn officer of the USS Westphalen in the 2380s, was a boomer. (Star Trek: Pendragon)