This scenario is best described as 'tailgating,' which is when an unauthorized individual gains access to a restricted area by following closely behind an authorized individual. It is a physical security breach that relies on social engineering tactics, exploiting politeness or inattention to breach a secure entrance. 'Piggybacking' sometimes is used interchangeably with 'tailgating', but it often implies that the authorized person is complicit in allowing the unauthorized individual access, while 'tailgating' suggests that the authorized individual is unaware of the security breach.