I love this HowlRound post not just because it gives me a newer, better piece of vocabulary: open-gender casting - the idea that a character can be played by an actor of either gender as their own gender. An example from my resume: playing Toby Belch as a female character. Another example of this would be a playwright writing characters with the intention that they can be played by either gender.
The other term I've been using as a catch all is cross-gender casting. Moving forward, I'll be using this term to describe scenarios where a character is played by an actor of the opposite gender as the gender of the character. An example from my resume: playing MacBeth as written, as a male character.
The post over at HowlRound by Susan Stroupe is intended as a conversation starter on this issue. So head on over, and make some comments!