A superlist is a grouping of a number of standard lists that already exist under the same domain. This does not change the underlying lists themselves, but when a message is posted to a superlist all the members of lists within that superlist receive a copy of the message. If a user is a member of more than one of these lists they will only receive one copy of the mail message, rather than once for
each list that they are a member of.
Superlists are a useful means of contacting the members of a number of lists with a single posting while at the same time eliminating duplication of messages.
A superlist is subject to the standard license limits that are in place for GMS Communication Server, i.e. the total (de-duplicated) members of all of the lists are totalled up and the license limit applied to this total, you can not therefore use a superlist as a means of circumnavigating the license limits of your installation.