Users can be locked out of their account if they try to login with the wrong password 8+ times.
Faculty and other Constituent accounts can be unlocked by Site Admins from within Constituent Manager. Find the Constituent, click on the "Account" tab, and look for the "Unlock User" link at the bottom of the page.
A confirmation window will popup, and refreshing the Account tab will show that the "Unlock User" link has disappeared.
Unlocking Site Admin Accounts
Site Admin accounts can be unlocked from the Admin Users screen, found on the "People" menu on the Composer left nav. Find the locked account in the "Group Users" section, click the right arrow button next to their name, and then click the "Unlock User" link.