When you type "fuck" and make a typo on a QWERTZ keyboard.
Was eventually coined as a mask word for the word it is a typo of.
Typo (QWERTY): Fyck.
Typo (QWERTZ): Fzck.
Comes from fuck, but when introduced to school-like invironments, it had to be changed to avoid troublements.
Oh, fzck, I didn't do my homework.
That guy is such a fzcking moron! Fzck!