Tailgating

One of the fraudulent authentication-based access methods where a person without permission to access a restricted zone enters the restricted zone following the preceding person who has access permissions.
Also called 'two-person entry,' tailgating is one of the most typical methods of gaining unauthorized access along with Piggybacking. Generally, tailgating refers to the act of gaining unauthorized access without intent, while piggybacking generally refers to the act of gaining unauthorized access with intent.