Freud proposed that psychological development in childhood takes place in a series of fixed stages. These are called psychosexual stages because each stage represents the fixation of libido (roughly translated as sexual drives or instincts) on a different area of the body. As a person grows physically certain areas of their body become important as sources of potential frustration (erogenous zones), pleasure or both. Freud believed that life was built round tension and pleasure. Freud also believed that all tension was due to the build up of libido (sexual energy) and that all pleasure came from its discharge.