Wiktionary
n. (context set theory English) The unique set that contains no elements. Notation: ∅ ''or'' {}
Wikipedia
Null set was once a common synonym for "empty set", but is now a technical term in measure theory. The empty set may also be called the void set.
Usage examples of "empty set".
His body writhed, smoked, then crumbled to dust, leaving an empty set of clothes behind.
Next she checks the empty set of saddlebags before placing one bag of powder in each saddlebag, carefully fastening the clasps.
He indicated an empty set of shackles to the right of Sergeant Rivera with a jab of his pike.
Perhaps she was, but she went into an empty set of rooms, and did not come out again.
Alucius had only seen the mill once, a cavernous and empty set of walls on the far west side of Iron Stem.
An ABC correspondent, not Diane or Charlie, was flying to Detroit to conduct the interview, rather than have them sit on an empty set with tiny plugs in their ears, talking to the air while someone back in New York asked the questions.