Wiktionary
alt. 1 (context idiomatic English) Something or someone in a group that is different or exceptional, that does not fit. 2 (context idiomatic English) A visual puzzle where the guesser has to choose which word/picture/symbol etc. does not fit with the others. n. 1 (context idiomatic English) Something or someone in a group that is different or exceptional, that does not fit. 2 (context idiomatic English) A visual puzzle where the guesser has to choose which word/picture/symbol etc. does not fit with the others.
Wikipedia
Odd One Out is a quiz programme hosted by Paul Daniels. It was broadcast weekly on BBC1 from 16 April 1982 to 19 April 1985. The show itself was a adaptation of the short-lived 1977 American game show called Knockout.
Usage examples of "odd one out".
Shanganagh was the odd one out, avoiding the other two until inexorable forces pulled her between their paths at Passover.
For you see, all the other students with Amas are already paired off, and you are the odd one out.