Twitter introduced Lists in 2009 to organize accounts and their tweets into curated groups.
Twitter Lists let users create or follow collections of accounts, such as journalists, sports teams, politicians, or friends. Instead of reading one universal timeline, a person could open a list and see tweets from only the accounts included in that group. Lists could be public, allowing others to discover and follow them, or private, for personal organization.
Twitter announced the feature in October 2009. Its purpose was to make Twitter easier to navigate as the number of accounts and conversations grew. A list does not merge tweets into a new social network or force users to unfollow anyone; it provides an additional, focused timeline.
Collections were a later curation feature for saving individual tweets, while Moments grouped tweets and media around major stories or events. Hashtags organize conversations by topic rather than maintaining a selected group of accounts. Those distinctions make Lists the canonical answer here.