Google canceled the Wave project. I guess even they couldn't figure out what it was and how it could work.
I have seen it, twice. Had no idea what it was for so I didn't bother. Google back then said that Wave is about to replace e-mail, and every other form of online communication. I guess they were wrong.
I still have access to my account. I used it a bit when it first came out. It was an interesting concept but I don't think people were ready for it. I suspect we will see it make a reappearance in the future.
Google wave is not actively developed but you can still login. You can check on http://wave.google.com/about.html if you want to know what it is/was.
Google Wave is... 1. You go to Google.com 2. Type "What is Google Wave?" on the search bar 3. Hit search 4. You educate yourself That is Google Wave.