A network mapping tool that pings IP addresses looking for a response and can discover host names, open communications ports, operating system names and versions. Written and maintained by Gordon Lyon, a.k.a. Fyodor, it is a free and open source software application used by both system admins and hackers alike and has been a staple in the security community for well over two decades.
CyberWire Glossary link: https://thecyberwire.com/glossary/nmap