what about boo like booing - shouting in disapproval examples from my dictionary is The crowd booed at the mention of the name The crowd booed the referee

It's not a mood or emotion but typically used when something doesn't go as planned. Here's an example below: Me: Can you go to the movies? You: No, I have to study. Me: Boo! Okay next time.

Third use of the word: used to startle or scare someone. My kids like to try to sneak up behind me and then yell "Boo!" to get me to shriek in surprise. We see it a lot around Halloween on decorations.

Hannah G.'s answer is correct; but there is also another use of the word. If you listen to rap or pop music in English, the performer will sometimes refer to their lover as "Boo" or "my Boo". This is more of a colloquial use, and isn't used in "formal" English speech.

Fourth use: A "boo boo" is a scrape or minor injury and we really only use it when taking to very small children. If a toddler falls and skins her knee we might ask her if she got a boo boo. I just remembered this use.