To fully understand the term Fluid mechanics we must first know what is Fluid and what is Mechanics.
The substances which have the tendency to flow or to move are known as Fluid.
Fluid includes liquids and gases.
Mechanics is the mechanism by which a substance behave.
Now You can easily understand the term Fluid Mechanics by simply considering above terms.
Fluid Mechanics is the branch of Engineering which deals with the study of mechanism related to fluids.
It may be defined as the mechanics of fluids including water.