Gatekeeper

Gatekeeper is an anti-malware feature of the macOS operating system. A user with administrator permissions can access the feature through the Security & Privacy panel of System Preferences.

History
The feature first appeared in Mac OS X 10.5 (Leopard) as File Quarantine. It was expanded in Mac OS X 10.6 (Snow Leopard) and became Gatekeeper in OS X 10.8 (Mountain Lion). Gatekeeper allows users to restrict which sources they can install applications from in order to reduce the likelihood of inadvertently executing a Trojan horse. There are three options: allow only applications downloaded from the Mac App Store to be launched, allow applications downloaded from the Mac App Store and applications signed by certified Apple developers to be launched, or allow all applications to be launched.