Like the topic says, what is XNA?

I've tried looking through the XNA website XNA Creators Club Online - home but since I'm downloading full speed at the same time it's slow as hell, so I havn't been able to surf through it freely :S

Anyways, from what I see and read, it looks like it's some WYSIWYG editor? I know it supports Xbox 360 and Windows and some Zune(?), and it does interest me if it's a 2D game engine, but NOT if it's WYSIWYG...
Also, I tried looking for some documentation on "What is XNA" still, I found nothing... Is it C++ at all?

Thanks in advance!