ip address help

Hello anyone,
I'm just trying to find what the term is called that referes to this way of writing an ip address:

192.168.100.0/12

i don't even know if i wrote that right...but what is it called when it is written with the "/12" part?? i'm trying to learn it, but i can't even look it up on any sites cause i have no idea what it's called or how to refer to it.

maybe if someone could even explain it a bit.

thanks!
-jes

It is called subnetting.

http://home.nyc.rr.com/computertaijutsu/subnet.html

I think this is what you're looking for...

http://www.fact-index.com/c/cl/class...n_routing.html

It just so happens that I recently learned about CIDR and the /xx-after-an-IP-address thing myself. :)

thanks both you guys!!
i actually already knew subnetting, i just didn't realize the /xx part was so easily related to it! :)