Socialism is a variety of social and economic systems characterised by social ownership and democratic control of the means of production; as well as the political ideologies, theories, and movements that aim at their establishment. Social ownership may refer to forms of public, cooperative, or collective ownership; to citizen ownership of equity; or to any combination of these. Although there are many varieties of socialism and there is no single definition encapsulating all of them, social ownership is the common element shared by its various forms.