Generally, any network connection that is opened and then is kept open in case it is needed again.
The Windows Internet Name Service (WINS) for Microsoft Windows 2000 Server uses persistent connections between WINS replication partners. Windows 2000 Server WINS replication partners maintain persistent connections among themselves so that replication can be initiated at any time without the network traffic overhead associated with establishing new connections. This means that WINS databases are updated immediately and shared network resources are always available.
In the earlier version of WINS for Windows NT Server, however, replication partners had to open a new connection between each other every time WINS replication was initiated. As a result, most administrators of large networks configured WINS replication to occur at certain time intervals or after a certain number of updates to the WINS database had accumulated. Because of delays in updating WINS databases on WINS servers, clients sometimes could not access shared network resources.