A "Sniffer" is a type of software or hardware tool used to monitor and analyze network traffic. It captures data packets that travel over a network, allowing users to inspect the information being sent and received. This can help in diagnosing network issues, ensuring security, and understanding network performance. Sniffers are commonly used by network administrators and cybersecurity professionals. They can identify unauthorized access, detect malicious activities, and troubleshoot connectivity problems. Popular examples of sniffer tools include Wireshark and tcpdump, which provide detailed insights into network communications and help maintain the integrity of computer networks.