As for an Email account or for Social networking sites like twitter and Facebook, user is recommended to have strong passwords which avoids phishing attacks. Hence Twitter added list of Banned Passwords to their source page for signup page of twitter .
Thus if you are signing up for new account in twitter, while you filling up account details twitter shows password strength indicator of your typed passwords either those are too obvious or weak comparing from their banned twitter passwords list. So twitter uses this list for passwords for Password Strength Indicator to Warne users to use strong passwords for their accounts during their signup process. If you are using any of these passwords in the list you can change to reasonable good password.
Any user can view the list of banned passwords by twitter by opening the source page of Twitter Signup page and by typing twttr.BANNED_PASSWORDS in Find box.
Thanks to The WunderCounter