Twitter Lists are like “groups”. They offer a way for you to bunch together other users on Twitter into groups so that you can get an overview of what they’re up to. That’s because Lists aren’t just static listings of users, but rather curated Twitter streams of the latest tweets from a specified set of users.
In other words, you can create a list that groups together people for whatever reason (the members of your family, for example), and then you can get a snapshot of the things those users are saying by viewing that list’s page, which includes a complete tweet stream for everyone on the list. Lists allow you to organize the people you’re following into groups, and they even allow you to include people you’re not following.