Role playing is the act of embodying a (usually) fictional character, either made-up by yourself or someone else, and acting out a narrative through the actions and dialogue of said character. You're also interacting with other characters and building a rapport with them. Not only are you telling a story with these other characters, but you're developing your own character.

The best role players truly connect and become their characters by knowing as much about their character as possible. You are expressing who they are, how they feel, their thoughts feelings, interests, passions, why they do the things they do. You can't be a character with knowing a character which is why, to me, character design is the most important part of role playing.