What does tgif stand for?

Silly me, I should have guessed this, but I didn’t know what TGIF stood for. Diamond on suggested, “Toes Go In First”, but that just confused me. Thankfully Google came to the rescue with the above link!
Moments later Kevin came up with the correct, “thank god it’s friday!” but then qualified his remark with, “well, not really, i’m an atheist. why would i thank some figment of mass hysteria about some arbitrary designation of time?”
Ann replied, “‘thank the anglo-saxons for the use of the phrase friday plus thank society for organising around a weekend’ just isn’t as catchy.’
Hmm.. I can’t repeat what Pron /msged me but the conversation degenerated quickly after that…