What do all those ports with FIN_WAIT_2 in "netstat -n" mean,

Essentially when a server receives a request to close a TCP
connection from a client, it replies to the client with a packet with
the FIN (for finish) bit set in the TCP header. The client then
replies to the server with a packet containing a ACK (for
acknowledge) bit in the header. The client then sends a packet a with
the FIN bit set in the TCP header, finally the server sends a packet
with an ACK bit set in the header and its all over and the port is
closed.