Does it mean anything when a man places his leg between a woman's when they're dancing?

There are certain dances that require the man to place his leg between the girl's legs during certain dance patterns. The tango [American, International and Argentine] is one type of dance where this occurs. Most latin dances do not require the man to put his leg between the girl's since these types of dances are generally danced apart. When I say this I'm referring to basic American or International social dancing. There can be exceptions if it has been choreographed into a routine for competition.

If this occurs during a "normal" social dance evening and such a move has little to do with the dance itself then it is time to get another dance partner because any guy who respects his partner and himself will not display this kind of conduct. Body language is very much part of dance and is a means of communication. Some of it can be inappropriate.

Ask the choreographer.