Unexpected Shutdown?

This morning when I went up to get on, my computer said something about a BSOD and an unexpected shutdown, I got in and everything seems to be fine, but I was wondering, what did that mean? Its never happened before, and avast! hasn’t blocked anything.
Help?

what did that mean?
you mean what is BSOD?

http://lmgtfy.com/?q=what+is+bsod

No, I mean, why did it shutdown?
I did some research on it: The Skype Application that makes you able to add phone numbers to skype via Internet Explorer 10 (I use Chrome as my main) had some weird glitch and gave my PC a BSOD. I guess its alright, it seems to be. Running an avast! scan detected nothing.