Dopamine is a type of neurotransmitter, which is a chemical messenger that transmits signals in the brain and other areas of the body. It plays several important roles in the body, and it's found in high levels in certain parts of the brain.
A group of neural structures responsible for incentive salience (i.e., motivation and "wanting", desire, or craving for a reward), associative learning (primarily positive reinforcement and classical conditioning), and positively-valenced emotions, particularly ones involving pleasure as a core component.