Social positions are "visible" if they require an individual to wear a uniform or some other kind of identifying mark. Often individual clothes or other attributes will advertise what social position one has at the moment. Non-visible social positions are called "hidden". A position that is deemed the most important to a given individual is called "central", others are "peripheral". If a "sequence of positions" is required to obtain a given position, it can be defined as a career, and a change of position in this context is a promotion or demotion. Some social positions may make it easier for a given person to obtain others; in other cases, some positions may be restricted to individuals meeting specific criteria.