In regular society, it refers to any system whereby new members are chosen; they cannot simply apply. In relation to websites and other technology-related organisations, the term refers to a more specific situation whereby invitations are sent, but there is never any approval needed from other members.
In regular society, it pertains to any system where new members are selected; they cannot apply directly. In relation to websites and other technology-related organizations, the term signifies a unique situation where invitations are issued but no approval is needed from current members.