Something that is unstable or subject to change can be described as fluid .
A liquid is a fluid — something that flows easily when poured — although gases can also be called fluid . When your doctor told you to drink lots of fluids to help your cold symptoms, she probably meant things like water or orange juice, not root beer floats. If a movement is smooth, it can also be described as fluid . You have to make fluid arm movements in ballet so you look graceful.