Historically, firewalls were literally walls that helped prevent fires from spreading. These walls are made from non-flammable material and are usually placed between a house and the garage so that any fire that starts inside the garage won’t reach the other areas.
The term firewall has also been adopted into Internet and computer lingo. Like the original firewall in homes it also acts as a defensive barrier in a computer or in a computer network.
The buzzword in the internet age is connectivity: computers are linked to the web or even in a local network in order to facilitate the exchange of information and sharing of files. While this certainly makes things faster and more convenient it can also make a computer vulnerable to a number of risks. Anyone can access files and even manipulate or destroy them.
In this scenario the firewall (whether a hardware or a software) acts as a filter which monitors for threats and then blocks them. Sometimes the firewall will also filter out even harmless files but people can adjust the filters accordingly. Different kinds of firewall software have different levels of customizability.
Some routers have a built in firewall function, but it is still recommended to install protective software. People or companies with high-security files should also take extra caution and not just rely on the firewall. In fact, it is recommended to keep important or sensitive documents in a separate, removeable hard drive and not in a computer that is linked 24-hours a day to the Internet.