iptables is a powerful tool used in Linux systems to manage network traffic. It acts as a firewall, allowing users to define rules that control incoming and outgoing data packets. By setting these rules, administrators can enhance security, block unwanted traffic, and permit only specific connections. The rules in iptables are organized into chains, which are groups of rules that determine how packets are handled. There are three main chains: INPUT, OUTPUT, and FORWARD. Each chain serves a different purpose, helping to filter traffic based on various criteria, such as source or destination IP addresses and protocols.