A social movement is a loose network of people who share common values which challenge traditional views of society in order to gain acceptance for these values. Examples are the feminist, gay or environmental movements.
There is no formal organisation or membership but people are instead in contact by means such as mobile phones and social media and meet on an ad hoc basis to discuss their aims and organise campaigns.
They tend to work through direct action and look to gain media attention rather than traditional interest group lobbying though pressure through means such as online petitions is also used.
Social movements have been seen as left-wing because they challenge traditional views but, as society has become more liberal, some political scientists point to right-wing movements that oppose these liberal attitudes.