What did List mean at Twitter?
Hi Saber, thanks for your question.
Twitter users can organize others into groups, or “lists”. When you click to view a list, you'll see a stream of Tweets from all the users included in that group. You can visit the Help Page from Twitter to get more detail explanation.
Is this like facebook directory
No. Facebook Directory is a directory that view every of your friends, pages and places, it is not organized or listed by you. Twitter lists is similar to Facebook list and Google+ stream.