Subnet

A subnet is a part of a larger network often divided into a CIDR range. A /24 and smaller is often called subnet where a larger can also be called a supernet. Pretend you are an organization that is connected to the Internet and you're given IP space from your uplink. Say you have a /24 which is 255 IP's. You may now subnet this /24 into four /26 networks so that accounting, sales, administration and dial-in pool get their own networks and are firewalled in between. A /26 is a subnet with 63 usable IP's.