A guest is someone who is visiting you or is at an event because you have invited them.

A guest is someone who visits a place or organization or appears on a radio or television show because they have been invited to do so.

A guest is someone who is staying in a hotel.

To guest means to take part in a performance or a match as a guest, rather than as a regular member.

If you say be my guest to someone, you are giving them permission to do something.