Conntrack is a subsystem of the Linux kernel's Netfilter framework that tracks the state of network connections passing through the system. It enables the operating system to monitor, manage, and filter network traffic by keeping a record of active connections, such as TCP, UDP, and ICMP sessions. Conntrack is essential for implementing stateful firewalls, as it allows rules to be applied based on the connection state (e.g., NEW, ESTABLISHED, RELATED). This improves security by enabling more granular control over which packets are allowed or blocked, preventing unauthorized access and mitigating certain types of attacks. Conntrack also provides tools and interfaces for administrators to view and manipulate connection tables.