Network Mapper, often referred to as Nmap, is a powerful open-source tool used for network discovery and security auditing. It allows users to identify devices on a network, determine their operating systems, and discover open ports. This information helps network administrators assess the security of their systems and identify potential vulnerabilities. Nmap operates by sending specially crafted packets to target devices and analyzing the responses. It can be used for various purposes, including network inventory, managing service upgrade schedules, and monitoring host or service uptime. Its versatility makes it a valuable resource for both security professionals and system administrators.