What is the meaning of Tailgate?

A hinged board or hatch at the rear of a vehicle that can be lowered for loading and unloading.

The hinged rear door of a hatchback.

Either of the downstream gates in a canal lock.

Ellipsis of tailgate party.

To drive dangerously close behind another vehicle.

To follow another person through access control on their access, rather than on one’s own credentials, especially when entering a door controlled by a card reader.

To privately purchase or sell a security immediately after trading in the same security for a client.

To have a tailgate party.

Source: wiktionary.org