fundamental

Fundamental is an adjective used to describe something that is essential, basic, or forming the foundation of a system, idea, or process. It is often used to indicate the underlying principles or elements that others build upon. The term comes from the Latin fundamentum, meaning foundation or base.

In science and mathematics, fundamental is used in several related senses. Fundamental constants refer to quantities thought to be universal and invariant, such as the speed of light in vacuum or elementary charges. Fundamental forces in physics are the four interactions—gravity, electromagnetism, the strong nuclear force, and the weak nuclear force—deemed to be the most basic interactions. A fundamental theorem or principle is a result that exposes a basic, widely applicable basis for a broader theory; for example, the fundamental theorem of calculus links differentiation and integration. In acoustics and signal processing, the fundamental frequency is the lowest frequency of a periodic waveform and largely determines the perceived pitch or tone.

In music, the fundamental note or pitch is the base tone from which overtones or harmonics arise. The overtone series explains how complex sounds are built from a fundamental frequency and higher harmonics. In biology and ecology, the concept of a fundamental niche describes the full set of environmental conditions under which a species can maintain populations, independent of biotic interactions; it contrasts with the realized niche.

In everyday language, fundamental is used to label ideas or aspects that are central or indispensable, such as fundamental rights, fundamental concepts, or fundamental changes. The term therefore spans practical usage across science, philosophy, policy, and everyday discourse.