An expletive and an adjective, "crap" can refer to something that's worthless or terrible. When someone calls something crap, they mean it's of very low quality.
"Crap" is a versatile word, often used as an expression of disappointment or disgust when things don't go as planned. You might hear someone say, "This concert was total crap," meaning the music wasn't good at all. On the other hand, if you're cooking and your dish turns out to be a disaster, you could call it "crap" too – in this case, the food isn't edible. As an adjective, "crap" can also describe something that's worthless or of poor quality: "This restaurant serves crap food." Just remember that "crap" is usually used informally and not in formal writing or polite conversation.
The husk of grain; chaff.
To defecate.
Example: That soup tasted funny, and now I need to crap.
(mildly) Of poor quality.
Example: I drove an old crap car for ten years before buying a new one.
Expression of worry, fear, shock, surprise, disgust, annoyance or dismay.
Example: Aw, crap, I have to start over again from the beginning of the level.
