"netstat -rn" for linux - what do the fields mean?

[CyberCowboy]

here's some output from the command netstat -rn:
Kernel IP routing table
Destination Gateway Genmask Flags MSS Window irtt Iface
10.0.1.0 0.0.0.0 255.255.255.0 U 40 0 0 eth0

i know what destination, Gateway, genmask, flags, and iface mean.

What do the MSS, Window, and irtt fields mean?
And what are they for?

 

[lowtech1]

-r = show routing table.

-n = show network addresses as numbers.

irtt = Initial Round Trip Time.

MSS = Maximum Segement Size for TCP connection.