warm prop
n. A person who appears in the background of a scene in a television show or movie.
Examples
1998
When you stick to a script, it's like you are just a warm prop.
—Matt Day, “Tell Your Mates About Unpredictable Kiss or Kill,” Asheville Citizen-Times, January 01, 1998
1997
So, what does the future hold for Simon Westaway? Bill Hughes, who certainly regards Westaway as more than just a warm prop, can see him branching out into other areas of film making.
—Rachel Browne, “My fabled career,” The Sun Herald, October 26, 1997
1995 (earliest)
Next come the aloof adolescents intent on hanging around the beach like warm props on Baywatch, who can barely manage to carry their own sunglasses.
—Kerry Cue, “Why do we love to live beside the seaside?,” The Advertiser, January 02, 1995
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