When you deactivate your Twitter account, your information is deleted 30 days later. You can reactivate your account during this period by signing in to Twitter with your username and password. Twitter automatically deactivates accounts determined to be inactive for more than six months.
Deleting Your Account Information
After logging in to Twitter and visiting your Account Settings page, you can delete your account by clicking “Deactivate My Account.” Several minutes later, your account is no longer publicly visible, but some of your past activity may appear on Twitter for several days or in Google or Bing search results indefinitely. Deactivating your account is possible only from the Twitter website, not from a mobile application.
Account Deleted Due to Inactivity
Twitter recommends logging in to your account and posting updates at least once every six months to keep your account active. You may not be able to tell if another user's account is active because her activity isn't necessarily publicly visible. If a Twitter user you currently follow doesn't post an update for more than six months, her account may still be active. If an account is deleted and you would like to use its username, you must wait for Twitter to release the inactive account's details.