The word "quantum" refers to a discrete amount or unit of something, especially in the context of physics and other sciences. It is commonly used to describe the smallest possible discrete unit of any physical property. In physics, for instance, quantum mechanics deals with the behavior of matter and energy on very small scales, such as atoms and subatomic particles.
The term "quantum" comes from the Latin word "quantus," which means "how much" or "how great." It has been used in English since the 19th century, primarily in scientific contexts.