Fluid (noun)

1. A substance that can flow and change its shape, such as a liquid or gas.
2. A substance that can flow easily, adaptable, changeable.

Origin:

Middle english: from old french fluide or latin fluidus, from fluere "to flow".

Examples:

1. The fluid in the container was red.
2. The fluid in the pipe was flowing.
3. The fluid in the engine needed to be changed.
4. The market is a fluid environment.
5. The company's plans are fluid and subject to change.