A person who dresses in clothes normally only associated with the opposite gender. A man who dresses in womens clothes is a male to female (MtF) crossdresser, a woman who dresses as a man is a female to male (FtM) crossdresser.
Crossdresser is often synonymous with the term transvestite
and both only refer to the clothes a person is wearing without making any comment on which gender the person acts as (this is related to transexuality
) or their sexuality