As Pratap said, it is sometimes used to indicate anger. If someone says/does something that the person doesn't like, the person might say, "what the hell!" In this sense, it means something like, "that was very rude/mean. How could you do that to me?!" It can also indicate general anger about a situation, rather than direct anger at another person. ---------- A second meaning is not about anger at all. Let me give an example to explain. Imagine someone is considering doing something that MIGHT end badly or be dangerous. The person considers the risks and rewards, and decides, sure, let's try! He might say, "What the hell, let's go!" ------------ It is important for you to know that this phrase is informal. You would not use it in formal writing or with people who might be offended. ----------- This is a complicated answer, so please feel free to ask for clarification.

just asking 'what' in an angry or annoyed manner.

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