One of the most requested features for Twitter over the past few years has been support for groups, which would provide a better way to organize the profiles you follow on Twitter. Twitter clients like TweetDeck have supported groups for a while now, and it is one of the main reasons why many people choose to use a Twitter client rather than the Twitter website.
In a blog post on Wednesday, Twitter announced they would finally support groups in the form of "Lists," which will be public by default, so other people could subscribe to your Lists. And Twitter clients won't be left out in the rain. The Twitter API will support Lists, so you will be able to see your custom groups in your favorite Twitter clients.
The ability to create Twitter lists means we'll have an easy means of segregating the profiles we follow. For example, you could create one list for friends and family, another for co-workers, another for NFL news or NFL players, another for newspapers like the NY Times and Washington Post, etc. This will make it much easier to check out just the information you are interested in at that moment.