Online

What is Online?

The term "online" refers to things that are on the Internet or that require an Internet connection to function. The antonym is offline.

For example, if a video is online, on Youtube for example, you need an Internet to watch it, because the video data isn't in your computer, it's on Youtube's computers, on the Internet. If a video is offline, this means you have downloaded a file that contains the video data to playback the entire video, and you can open it in a video player without requiring Internet connection.

What is "To Be Online"?

To be online means to be connected to the Internet, or, more specifically, to a specific online communication service, such as a chatting app. If you are online on Facebook, for example, that means other people can send messages to you and you would be able to respond to them in real time, immediately after receiving the message. If you were offline, you wouldn't know about the messages until you connected to the Internet AND opened Facebook, or you had a Facebook app installed in your computer (smartphone) that automatically connected to the Internet and checked new messages without you having to open Facebook.

In general, it's possible to tell others you don't want to be disturbed temporarily by making your "status" on the chatting app "Do Not Disturb," however, that doesn't mean you're offline, or unreachable, that just means you don't want to be disturbed, and some people may not respect that. Consequently, chatting platforms also allow online users to mark themselves as offline even if they are online, so that other people can't see that they are online, even when they are.