A state of matter characterized by a fixed amount of space it occupies, yet lacking a consistent form and conforming to the shape of its container. Water in a glass, oil in an engine, and molten metal are common examples. The constituent particles are close together but are able to move past one another, allowing it to flow and adapt to the surrounding environment.
Understanding this particular state of matter is fundamental to various scientific and engineering disciplines. Its properties are critical in fluid dynamics, chemical processes, and material science, influencing everything from designing efficient pipelines to developing new types of lubricants. The study of these substances dates back to ancient observations of water and other liquids, eventually leading to the development of sophisticated models and theories describing their behavior.