The word firewall originally refered to a wall of fireproof material intended to prevent a fire from spreading within a row of buildings in the 1600’s. These walls separated two parts of a building from the basement to the roof. Later the word firewall was used to refer to a metal sheet separating the engine compartment from the passenger compartment of a vehicle or plane.
In the late 1980s, when the internet was relatively new, the word firewall started to be used to describe network security routers. These routers were the predecessors of modern firewalls.
Today a firewall is a hardware or software device designed to protect your computer network. The firewall does this by monitoring and filtering incoming and outgoing network traffic. It has the ability to block suspicious traffic and it decides whether to or not to do so based on a defined set of security rules. The purpose of a firewall is to prevent outsiders from gaining unauthorized access to the private data on your computer network. Firewalls have been a first line of defense in network security for over 25 years. You can think of a Firewall as a barrier between a trusted network and an untrusted network. Kind of like a wall of fireproof material made to keep a fire from spreading!