Membership is a means by which an organization or government determines its core constituency---and excludes non-members. Members enjoy some specific set of rights of governance and benefit that non-members do not enjoy. In state contexts, it is generally referred to as citizenship. In corporate contexts, it may correlate with stock ownership. Systems of membership typically presume some means of identity management.
Input: identity management, set of membership rights and benefits
Output: enjoyment of rights and benefits by members