The client ID and client secret are your application's credentials.
Partner applications have two unique identifiers: ApplicationIdentifier (client ID) and ApplicationToken (client secret). The latter is considered a password and must be stored as such.
Client ID - ApplicationIdentifier
Uniquely identifies the application used, and used by the SuperOffice CRM Online to know where to redirect a user.
Client secret - ApplicationToken
Must be supplied when invoking any of the SuperOffice CRM Online web services.