What are removable circuit boards inserted into slots in the motherboard called?

Removable circuit boards that are inserted into slots on a motherboard are commonly referred to as cards. These cards can serve various functions and can be added or removed based on the user's needs. For example, graphics cards enhance video performance, sound cards improve audio capabilities, and network cards provide connectivity options.

The use of the term "cards" emphasizes their modular nature, allowing for easy upgrades or replacements of specific components without needing to change the entire motherboard. This modular design is fundamental in modern computing, as it gives users flexibility in customizing their system's capabilities according to their requirements.

Other terms such as modules, circuits, or chips are often used in different contexts or may refer to other components but do not accurately describe the specific nature of removable circuit boards in this context. This distinction makes "cards" the correct and most appropriate answer.