If an application that communicates with a remote system as a normal part of its operation but is in a state where it is unable to communicate with that remote system, it is in an "offline" state.
Questions dealing with "offline" focus on the operation of an application when it is unable to communicate with a remote host and that communication is essential to the operation of the application.
The goal of operating in offline mode is to provide smooth operation even in the absence of an essential part of the system. The user should be either unaware or minimally aware that core functionality is missing or delayed.
For example: a web application running in a browser that manages web-based email might still be able to perform limited operations when offline, queuing operations. Then when the remote host is accessible, it may sync with the host and perform those queued operations.
