Most commonly defined at present as 'the scientific study of MIND and BEHAVIOUR'. No dictionary on the subject is content to leave it there, however, and one such volume (admittedly with claims to being 'comprehensive') goes on and on about it for seven pages. But no definition of such an enormously wide-ranging subject will satisfy every psychologist. Indeed one dictionary claims that 'psychology simply cannot be defined'. My own opinion is that 'the scientific study of mind and behaviour' most accurately describes the route to increasing our psychological knowledge (behaviour) while it focuses on a psychological understanding of what that behaviour is about and how to make sense of it (mind).