Netsplit

In computer networking, mainly Internet Relay Chat (IRC), netsplit is the event when two servers disconnect. Because how IRC networks are built, a disconnection between two servers splits the entire network into two parts. This makes it look like people on the other half of the network have quit from IRC.
Appearance of netsplits.
Below is an example of typical netsplit. When two servers split, a user sees this as large number of users quitting. After the servers are reconnected, a user sees the other users rejoining.