What is the name of the component that holds two cars together?

The correct answer is the coupler. A coupler is a mechanical device used to connect two train cars together, allowing them to operate as a single unit while enabling flexibility for movement. Couplers are designed to ensure that the connection is secure, allowing for safe transport of cargo or passengers without risk of disengagement during travel.

In the context of rail systems, couplers also have features that allow them to absorb shocks and provide a safe distance between cars when the train is in motion. This component is essential in maintaining the integrity of a train's structure and ensuring safe operations.

Other terms like linkage, connector, and fastener might describe elements of connections in different contexts but do not specifically represent the device used on trains for connecting cars. For instance, a linkage might refer to a system that connects various components of machinery, while a connector may imply a more general joining mechanism, and a fastener typically refers to devices used to secure parts in a stationary manner.