Firewall is hardware or software or both that helps protect your system connected on the network from untrusted sites that may contain viruses or other malware.
Features of Firewall
Firewall allows or blocks access to particular website based on set of pre-defined rules.
Firewall enhances the security feature of the system connected to the network on the internet.
Firewall protects your laptop or mobile when connecting to internet via public wi-fi such as railway-station or airport free wi-fi.