A coachload is a group of people travelling together in a coach — here a long bus for trips, not a sports teacher. People say it especially when that bus is full, or when they want you to picture a whole bus of people arriving at once. You will hear it a lot in British English: a coachload of tourists, coachloads of shoppers. There is often a little extra feeling with it, not always kind, that a big crowd has landed in a small place. Americans are more likely to say a busload.