Peer pressure is pressure exerted upon someone (or some entity) by their (or its) peers. It is most visible in (but definitely not limited to !) groups of young people, and it is the driving force behind popular culture.
It can be overt or insidious, and both forms effect anyone who interacts with others at all times they are doing so. It can be on any type of scale and is seen in the way that huge corporations exploit it for their own benefit, and in school classrooms where social rank is ordered by the clothes students wear and the way they talk.
It is also broadcast in music, in television and in film, extending the Westernisation (Americanisation?) of large groups of young people and giving them an ironic sense of nonconformity. It is the driving force behind pop culture and great evidence of this are the meaningless fads and icons produced by the industry that are eaten up by the adoring public.