Zenmap is the graphical User Interface representation for NMAP Security Scanner. It is an open-source program designed to make NMAP easy for starters to use. Typically, it is used to collect and identify a list of hosts, OS, as well what services are running on them by using a port scanning tool. It is used specifically for the scanning and vulnerability phase of ethical hacking.
A network administrator who wishes to audit all the devices on a specific IP scheme in a network can use NMAP. The admin can go ahead and scan the ports to know exactly which ports are closed and which are opened.