Question is in the title, really.
What is the definition of cross-dressing?
Is it just wearing clothes that "mainstream culture" would deem as belonging to the opposite sex?
Or does it have to have an element of sexual titillation or "expressing your inner woman/man" or something?
Or to rephrase:
If I wear my husbands underpants (in Germany we call them Boxershorts, I'm not sure if they are called the same in english?) because they are more comfortable than the woman's "boyshorts", or if I buy a pyjama top from the men's collection because it's warmer and has a more covering neckline, do I cross dress?
If my husband wears a sarong-style skirt in the house when the temperature gets really high in summer, is that cross dressing?