The concept of crossdressing?

[Samantha W]

I think it comes down to my Signature line.

[carhill2mn]

The term began as a derivative of the medical term Transvestite (from the Latin for trans = across and vestment = clothing). Transvestite began to denote someone with a fetish, a sexual attachment to the clothing of the opposite sex and became derogatory. Those that wished to divest themselves from this classification began using the term Crossdresser.
Now things have evolved to TG which is less derogatory and more directed at defining someone who emotionally, psychologically leans more toward opposite sex and refers less to the aspect of clothing.
All the terms coexist, but in people's minds have differing connotations.

Cheryl is basically correct. Virgina Prince (who was a pioneer, of sorts, in this area) tried to get some terms other than transvestite to be used but was not very successful. Transvestite is still widely used outside of the United States. "Crossdresser" evolved as being more "acceptable" for people in the U.S. Unfortunately, for many years medical books (and others) have associated sexual stimulation with the term "transvestite". This was another reason that "crossdresser" became more popular as it was, in many cases, more accurate.