Two-step verification is a type of two-factor authentication offered on Google accounts, including VT Google Apps. Many online services such as Google, Facebook, and Twitter offer this as an added layer of security to your online account.
Two-step verification requires you, the account owner, to obtain and input a different, one-time use, code each time you sign into your account. This helps prevent other people from accessing your account, because the person would need to have both your password and the special code. For more information on the creating and using two-step verification with your VT Google Apps account, see Google's About 2-step verification page.