The social accounts this site is allowed to publish to.
A connection is not permanent
The permission a social network grants has an expiry. An account can move to expired without anyone doing anything, and without any warning from the network itself.
Posts sent to an expired account fail. So when publishing fails for no apparent reason, the account status is the first place to look — not the post's text.
Four states
Connected means it works. Expired means the permission has run out and it must be reconnected. Disconnected means you, or the network, removed the connection. Error means the last attempt came back unsuccessful.
Connecting requires platform-level settings
Before an account can be connected, each network's application credentials must be recorded in the system settings. Until they are, that network shows as not configured and its connect button does nothing.
Those settings belong to the whole install, not to a single user.