A Z-lister is a person at the very bottom of the fame ladder — someone who turns up on television or in magazines but who almost nobody really thinks of as a star. It is the noun that goes with the adjective Z-list. English ranks famous people with letters: A-list is the top, the real stars, and the alphabet runs down from there. Z is the last letter, so a Z-lister is as far from the top as you can go. Two kinds of people get called this. One is the barely-known: an actor who has had three small parts, a singer nobody outside one city has heard. The other kind — and this is the one people usually mean — is someone who is genuinely all over the newspapers but has done nothing to earn it. They were on a reality show. They dated somebody famous. They are famous for being famous. That second meaning carries real scorn: the speaker is saying this person takes up space that should belong to someone with talent. The word is informal and it is rude. Gossip magazines and British newspapers throw it around freely, but you would not use it about someone to their face, and it does not belong in serious writing. It is often said with a little sniff of superiority, which is why it can sound snobbish as well as unkind. You will also see it stretched beyond show business, half in fun — a Z-lister at a conference, meaning the least important person in the room.