Many Spanish people don't know how to say this word properly in English.
They often use the word "sign" or something similar. "Sign" means "firmar" in Spanish. The correct translation is "subject".
So, for example: "How many subjects did you study at school?" or "What was your favorite subject at school?".
I hope that helps.
Soy el director de Daniel Smith + Partners. Tengo más de 15 años de experiencia enseñando inglés a españoles.