A recipient of hospitality, specifically someone staying by invitation at the house of another.

“The guests were let in by the butler.”

A patron or customer in a hotel etc.

“Guests must vacate their rooms by 10 o'clock on their day of departure.”

An invited visitor or performer to an institution or to a broadcast.

“The guest for the broadcast was a leading footballer.”

To appear as a guest, especially on a broadcast

As a musician, to play as a guest, providing an instrument that a band/orchestra does not normally have in its line up (for instance, percussion in a string band)

To receive or entertain hospitably.