What is a subnet?
A subnet, or a subnetwork, is simply a network within a network. It's basically a shortcut that the network traffic can take to get to the desired destination faster.
Let's say you want to visit a website. As there can be millions of devices connected to a network, it would take a long time to find the correct device. Subnetting minimizes the traffic by narrowing down the possible IP addresses within a range of devices.
Each IP address has two fields, network ID and host ID. For instance, if an IP is 18.104.22.168/16, the network ID would be 95.120 and the host ID is 0.0. The subnet will then use the host ID to find the individual subnets.