Tailgaiting is when an unauthorized person "tails" an authorized person through a secured entryway without the authorized person's knowledge.
In security, piggybacking, contrasted with tailgating, refers to when a person tags along with another person who is authorized to gain entry into a restricted area, or pass a certain checkpoint. The act may be legal or illegal, authorized or unauthorized, depending on the circumstances. However, the term more often has the connotation of being an illegal or unauthorized act.
To describe the act of an unauthorized person who follows someone to a restricted area without …