An organization is a group of individuals that are members of a common group. Community membership can be assigned on an organization membership basis. Once an employee is a member of an organization, that employee has access to all communities that the organization belongs to. For example, all HR employees might be members of the HR organization. You could add a new hire to the HR organization, and that new hire would automatically receive membership to all the communities in which the HR organization has membership. You can designate an organization to have guest, member, or leader access to a community.