What does /24 means in nmap scanning?

Question

I have just started learning about the use of nmap and while doing so, I am unable to find much information on a particular command.

This is the command I am using: nmap -sP 192.168.100.0/24 to scan for the list of connected devices on the network.

While the ip address used is the subnet ip, I am having trouble understanding what /24 does.

Can someone kindly share any insights to me?

Answer 1

/24 specifies the netmask to use -- 24 bits in this case, so a mask of 255.255.255.0. So it will scan all addresses from 192.168.100.0 to 192.168.100.255