Offline refers to when a user is working without an active internet connection. This means there is no transfer of data from the client device to the server, affecting real time updates and concurrency issues.
"Offline" scenarios mean a user and their data is not directly controlled by or connected to a computer or the Internet. In a variety of contexts this could mean a user is gathering data on paper systems, or is entering digital data into a device that does not have the capacity to send it to its intended destination at that moment in time.
Offline technologies have to consider local storage, or caching to overcome this limitation, until the user can get "online" and transfer the information over.