A composite character is when a character in a story is made up of different parts or traits from multiple characters. So imagine if you were making a recipe for a character - instead of just using ingredients from one character, you might take a little bit from different characters to create a new one. It's kind of like making a Frankenstein's monster, but with personality traits instead of body parts. The new character might have the bravery of one character, the humor of another, and the intelligence of a third. It's a way to make a new, interesting character that has qualities from different people.