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Where is the link back to ubuntu.stackexchange.com from meta.ubuntu.stackexchange.com?
The other answer looks out-of-date now. Here is an updated screenshot I took; the link you want is now called main:
It's called parent. Left of faq in the navigation bar right at the top.
It's not always right of the log out link. Get 2000 reputation and it's right of a tools link: