Metaphor is a term for a figure of speech. It does not use a word in its basic literal sense. Instead, it uses a word in a kind of comparison. We run, and we also say rivers run. We may run into trouble, especially if we run up a bill at the bar.

So a metaphor uses words to make a picture in our mind. It takes a word from its original context, and uses it in another.

"I beat him with a stick" = literal meaning of 'beat'.

"I beat him in an argument" = metaphorical meaning of 'beat'.