The tooltip when hovering "Meta Stack Overflow" in the footer is right now:
the Stack Exchange engine powering these sites
Proof just in case it's fixed:
It appears that other sites' tooltip is taken from their About page e.g. Mathematics where the formula is:
[site name] is a question and answer site for [target audience]. It's built and run by you...
And the tooltip is taking the [target audience] of the site.
According to this logic, it can be the following for this Meta site:
meta-discussion of the Stack Exchange family of Q&A websites