What is described as a printed circuit board that can be inserted into an electrical connector?

An expansion board, also known as an expansion card, is specifically designed to be inserted into an electrical connector or slot on a motherboard, allowing the enhancement of a computer's capabilities. These boards can provide additional functionality, such as improved graphics performance, sound processing, additional ports, or networking capabilities.

Expansion boards often come in standardized sizes and formats, like PCI or PCIe, ensuring compatibility with the motherboard's connectors. This feature of being easily added or removed makes them distinct and very useful for upgrading computers or customizing them according to specific needs.

The other terms refer to different components or functionalities. A motherboard is the main circuit board connecting all essential components; a control unit is part of the CPU responsible for directing operations; and an interface board often serves to connect different types of equipment or systems, rather than expanding capabilities. Thus, the definition provided aligns perfectly with the description of an expansion board.