This directive enables or disables resetting the connection upon timeout. When resetting the connection, before the socket is closed, the SO_LINGER option is set to the socket with timeout value of 0, which forces RST packet to be sent to client upon closing the socket, while all memory associated with the socket is freed. This allows to avoid the situation when the already closed socket is in the FIN_WAIT1 state with the loaded buffers.
The keepalive connections, after timeout, are closed in the usual way.