A port scanner is a tool used to identify open ports and services on a computer or network. It sends requests to various ports on a target system and analyzes the responses to determine which ports are active. This information can help network administrators assess security and troubleshoot connectivity issues. Port scanning is often used in cybersecurity to detect vulnerabilities in a system. By identifying open ports, security professionals can better understand potential entry points for unauthorized access. However, it can also be misused by malicious actors to exploit weaknesses in a network, making it essential to monitor and secure open ports effectively.