What's a ringer?
Someone with significant prior dance experience which is played down for the cameras
So, even though the person hasn't done ballroom or latin, they have enough experience working with a choreographer or team, attending stage school, or lessons to give them a significant advantage on such things as keeping to the beat, rhythm, timing, and flair.
Ringers include :
Tom Chambers
Denise Van Outen
I think we all insisted Karim was a ringer.
I say Kym is a ringer because she did Popstars and when she did it, she had been trying to make it for some time, very well supported by parents, and had done all the standard extra curriculars of someone trying to get into showbiz. So, a massive advantage against a beginner like Tony Adams.
Someone else will be along with more names.