What is hentai

So me and my dad was watching TV and I asked him if I could watch anime. He said "I dont want to watch that narudo hentai stuff" I looked at him and was like what the fuck did u just say anyway I ignored him cuz I could have heard him wrong. So like 3 months later I was watching the anime gansta (good show u should watch it) he came in the room and asked me what is hentai I laughed and changed the subject. I'm afraid he is going to ask again and get mad if I answer and I know what that is. If he looks it up he will be mad if I tell him he will be mad either way I'm getting my ass whooped.