A software firewall is a program installed on a computer or network device that monitors and controls incoming and outgoing network traffic. It acts as a barrier between a trusted internal network and untrusted external networks, such as the Internet. By analyzing data packets, it can block or allow traffic based on predetermined security rules. Unlike hardware firewalls, which are physical devices, software firewalls are flexible and can be customized for individual devices. They are commonly used in personal computers and servers to protect against unauthorized access, malware, and other cyber threats, ensuring a safer online experience for users.