It’s a passed through socket option determining the number of connections queued.
- http://docs.oracle.com/javase/7/docs/api/java/net/ServerSocket.html
The maximum queue length for incoming connection indications (a request to connect) is set to the backlog parameter. If a connection indication arrives when the queue is full, the connection is refused.
- More on netty channels: http://seeallhearall.blogspot.de/2012/06/netty-tutorial-part-15-on-channel.html