Generally, I think moredes refers to tashmish. The Rambam seems to also include certain melachos that women are supposed to do for their husbands into the category, as well. (Husbands also have obligations to support their wives in return.)
A man can also be a mored in the area of tashmish, as well. Either side can call beis din if they feel they are being denied their rights. It becomes tricky if one side says the other is being mored, but the other side says they are together in a normal marital framework. Beis Din can’t send eidim into the room.
One thing to note is that while a man can divorce his wife if he claims she is a moredes, beis din would not grant a woman a divorce for making that claim, since they would be chosesh that maybe she set her eyes upon another man. i.e., maybe she is making up a lie to get herself a divorce so she can marry somebody she developed an attraction for. It is very complex how beis din can verify the truth.