Whereas a firewall in building structural terms is designed to resist the passage of something undesirable such as fire from one side to another, a firewall in technology is designed to specifically resist the passage of undesirable network traffic. Unlike building firewalls however, network firewalls have many sides and can protect devices on any one side.
Firewalls can either be network-based or personal. A network-based firewall is a dedicated piece of hardware and software installed on a network to protect a number of computer servers and/or workstations. On the other hand, a personal firewall is a piece of software that resides on an individual workstation to protect it.