who is freud?
Freud is Sigmund Freud, an Austrian neurologist who founded psychoanalysis as a treatment for psychopathology (you can read the wikipedia page about him here).
He’s also the one behind the Oedipus Complex, which basically claims that all boys are sexually attracted to their mothers when they’re babies, and the Electra Complex, which is the same only for girls being attracted their fathers. Of course it’s more complicated than that but that’s pretty much the highlight of it.
As you can imagine, it’s generally rejected in academic circles but that’s what all the jokes about Freud in the ace community are about. If your interested you can read about the Oedipus and Electra Complexes here and some more of Freud’s ideas here.
I hope this helps and I hope you’re fortunate enough to never have to study this man in an academic setting (I, unfortunately, was not so lucky).