Attack Surface

Attack surface↗ is the complete set of points where an unauthorized user could try to enter data into, or extract data from, an environment, every exposed API, open port, web form, user account, and piece of software. The larger and more complex a system, the more potential entry points an attacker has to work with.

Reducing attack surface, by disabling unused services, removing unnecessary accounts, and limiting what's exposed to the internet, is one of the most effective ways to lower risk, since attackers can't exploit↗ a door that isn't there.