Archiving a client removes the client from most dropdown lists and preserves their information. You would archive a client if you are no longer providing a service to the client for example.
You are able to search for clients that have been archived. This is how you can do it:
You will now see a list of all archived clients which will allow you to access the client record or you can easily unarchive the client by clicking "Unarchive" from the list.
If an archived client needs to be reactivated, you can do this by first following the steps above to search for and to access the archived client. You can then unarchive the client in the client's record by accessing 'Admin' selecting "Unarchive" and saving the setting.