A relatively new word in the psychology world, it's not in the DSM-IV-TR (a book that a couselor would use for a diagnosis). People pleasers are doormats who let high expectations, resentment, and saying yes when they mean no run their lives. They are set on being perfect and nice. It affects mostly women because they are socialized to do for other people instead of for themselves. This has also been linked to codependence.
Woman 1: "Let's ask Kate to do the bake sale. She never says no."
Woman 2:"She's such a people pleaser."