What term is used for turning a guest away from the hotel due to overbooking?

The term when hotels turn guests away because their rooms are overbooked is called "walking" or "walked".

Overbooking is a situation where a business sells a good or service when the supply for this transaction is actually not available.

Overbooking can happen when current guests increase their stay without further notice or when a room is not proper for a guest to stay in. It can also happen when hotels purposefully gave a room during busy seasons to more than one guest - thinking that perhaps one of them might cancel.