A firewall is a security system that monitors and controls incoming and outgoing network traffic. It acts like a barrier between a trusted internal network and untrusted external networks, such as the Internet. By filtering data packets, a firewall helps protect computers and networks from unauthorized access and cyber threats. There are two main types of firewalls: hardware firewalls, which are physical devices placed between a network and its connection to the Internet, and software firewalls, which are programs installed on individual computers. Both types work together to ensure that only safe and legitimate traffic is allowed through, keeping your data secure.