Difference between deactivate and freeze user in salesforce

In some cases, you can’t immediately deactivate a user such as when a user is selected in a custom hierarchy field or a user that’s assigned as the sole recipient of a workflow email alert. To prevent users from logging into your organization while you perform the steps to deactivate them you can freeze users.

• Freezing user doesn’t make their user licenses available for use in your organization.
• Deactivating a user will be available user licenses available for use in your organization.