This question already has an answer here:
I've seen an answer from my questions like Why didn't McGonagall send only Parkinson to the dungeons?
What I'm referring to is
Well, the movies are nonsense, but putting that to one side... Out of universe it's a sarcastic joke and that may even be part of it in universe as well. A bit of humour to relieve the tension before the battle. I don't think, in-universe, the Slytherins were ever actually taken to the dungeons, McGonagall was clearly being snarky and sarcastic.
But I've seen questions mentioning "Out of Universe" from this website. I researched for this meaning but I don't understand it. So please help me. =)