noun
A general term for substances that flow, including liquids and gases. Often used in scientific or technical contexts.
水は流動体の一種です。
Water is a type of fluid.
流動体の性質を調べる実験を
We conducted an experiment to investigate the properties of fluids.
流体 is a more common and general term for 'fluid' in physics and engineering. 流動体 is less frequent and may sound slightly more formal or technical.
Compound of 流動 (flow, movement) and 体 (body, substance). The exact historical derivation is uncertain, but the word follows a common pattern for technical terms in modern Japanese.