SimplePie problem

I am getting the SimplePie memory errors that are mentioned in many places on the forums, and I understand how to increase memory. What I don’t understand is–where did SimplePie come from? Is it part of a standard new 3.5.1 install? I don’t see it in the installed plugins on my dashboard and, so far as I know, I don’t need it and didn’t put it there. Hmmmmmm?

Thanks!
Krista