A stateless firewall is a type of network security device that filters traffic based on predefined rules without keeping track of the state of active connections. It examines each packet individually, allowing or blocking it based solely on the information contained in the packet headers, such as source and destination IP addresses and port numbers. Unlike stateful firewalls, which monitor the state of active connections and make decisions based on the context of the traffic, stateless firewalls are simpler and faster. They are often used in situations where speed is crucial, such as in routers or network appliances, but may offer less security than their stateful counterparts.