Lists are groups of Twitter users you can create (and name) for everyone to see and follow. To quote Twitter, “Lists are timelines you build yourself, consisting of friends, family, co-workers, sports teams, you name it.” You can also create private lists which can be accessed by you only.
Lists are different from ‘groups’ since lists behave more like individual users — you can follow/unfollow lists. Once you start following a list, updates from the users in the list will appear in your timeline. But lists can be used as groups to sort people whom you follow and see what they are talking about.