The longer answer
Yardage is the trap world's handicap system. Where a golfer carries a number that shrinks as they get better, a trap shooter carries a yardage that grows — the better you shoot at registered events, the further back the rules push you. Singles is always shot from 16 yards; handicap distances begin at 17 and reach all the way to 27, awarded in small increments called punches.
Yardage is durable. Punches happen at registered ATA events and accumulate on a shooter's ATA card; every registered handicap event they enter afterwards is shot from that distance. A 24-yard shooter is a 24-yard shooter at every club in the country until they earn the next half-yard back.