What do all these memory letters represent?
Recv-Q Send-Q 0 0 mem:(r0,w0,f0,t0)
You can do man netstat to understand what Recv-Q and Send-Q mean:
The count of bytes not copied by the user program connected to this socket.
The count of bytes not acknowledged by the remote host.
The rmem, wmem, fmem, and tmem refers to specific Linux kernel values:
rmem = sk->sk_rmem_alloc;
wmem = sk->sk_wmem_queued;
fmem = sk->sk_forward_alloc;
tmem = sk->sk_wmem_alloc;
For more information, see Chapter 9 of TCP/IP Architecture, Design and Implementation in Linux: