What are cards that expand a computer’s functions called?

The term for cards that expand a computer's functions is "adapter cards." These are printed circuit boards that can be installed into an expansion slot on a motherboard, allowing the system to add new capabilities such as enhanced graphics, sound, networking, or additional storage capabilities.

Adapter cards are essential for customizing and upgrading a computer's performance beyond what the original system offers. For example, a graphics adapter card can significantly boost the visual capabilities of a computer, making it suitable for gaming or graphic design.

In contrast, interface cables are used to connect different components but do not expand functionality on their own. Power supplies provide the necessary electrical power for the system’s components but do not impart additional functions. Motherboards serve as the main circuit board that connects and communicates with all components of the computer, but they do not themselves expand functions; instead, they host adapter cards that provide such expansion.