A visitor to any of the Disney theme parks

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

A patron or customer in a hotel etc.

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

(computing) A user given temporary access to a system despite not having an account of their own.

(zoology) Any insect that lives in the nest of another without compulsion and usually not as a parasite.

(zoology) An inquiline.

(intransitive) To appear as a guest, especially on a broadcast.

(intransitive) 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).