Offline caching typically means storing locally the data obtained from a remote service to make it possible to browse the data even when there is no connection to the storage.
The details of the implementation depend on actual needs of the application; however, in any implementation there is a local cache of data obtained from the service, so some requests for the remote data may succeed in that cache. It depends on the application logic how the cache is updated, and whether and how the user may control that.
A good example of an application that uses offline caching is a desktop e-mail client. It downloads all new mail from the server to the user's computer during the sync session; the user may browse the mail and write the replies; the outgoing mail will be sent when the application perfoms the next sync.
