A software created to scan your computer and remove computer viruses including Trojan, spyware, adware, keylogger, hoax and other variants of malware. It also provides protection from attacks of computer threats.

I think that it is a synonym for anti virus program. That is it is a program designed to remove viruses, trojans, malwares, spywares and other unwanted materials and also to provide firewall facilities.

Or it could be the person who makes anti virus.