[man 7 tcp]
http://www.die.net/doc/linux/man/man7/tcp.7.html

[ipsysctl]
http://ipsysctl-tutorial.frozentux.net/chunkyhtml/index.html

...

The state of the socket. Since there are no states in raw mode and usually no states
used in UDP, this column may be left blank. Normally this can be one of several
values: 


ESTABLISHED 
The socket has an established connection. 

SYN_SENT 
The socket is actively attempting to establish a connection. 

SYN_RECV 
A connection request has been received from the network. 

FIN_WAIT1 
The socket is closed, and the connection is shutting down. 

FIN_WAIT2 
Connection is closed, and the socket is waiting for a shutdown from the remote end.


TIME_WAIT 
The socket is waiting after close to handle packets still in the network. 

CLOSED 
The socket is not being used. 

CLOSE_WAIT 
The remote end has shut down, waiting for the socket to close. 

LAST_ACK 
The remote end has shut down, and the socket is closed. Waiting for acknowledgement.


LISTEN 
The socket is listening for incoming connections. Such sockets are not included in
the output unless you specify the --listening (-l) or --all (-a) option. 

CLOSING 
Both sockets are shut down but we still don't have all our data sent. 

UNKNOWN 
The state of the socket is unknown.