What is "Rich text with HTML"?

I can choose that option when I should send an e-mail to someone on my forum! What is it?

Bump

Rich text means it's HTML enabled.

Plain text is well, text.

right it means you can use html coding
not everyone email may read html depending on there setting so is best to use regular.

be it depends what you are sending.

Can I use BB-codes in Rich Text too, or can I only use HTML?

no, not that i know of, i think BB-code of only for forums.