Freezing user accounts
This feature allows you to freeze user records. Often there are times when you may not want to deactivate a user immediately (such as when a user is part of an approval process) but you must prevent them from logging into your organization (as they have left the company, for example) while you perform the steps to deactivate them.
To freeze a user record, navigate to Setup | Manage Users | Users. Now, click on a user's name to access their user detail page. Now click the Freeze button.