What are some examples of fluid flow?
A river flowing down a mountain; air passing over a bird's wing; blood moving through a circulatory system; fuel moving through an engine. These are all examples of fluid flow.
A fluid is a substance that conforms to the shape of whatever vessel contains them. For instance, if you take water from a jar and pour it into a tea kettle, it will change from a jar shaped mass to a tea kettle shaped mass.
In this sense, any liquid or gas can be classified as a fluid, and this article defines fluid flow as, "motion of a fluid subjected to unbalanced forces or stresses."
Imagine a jar full of water tipped over. The fluid at the bottom of the jar is held up against gravity, and therefore does not fall. The forces acting on this fluid are balanced. The water at the top, however, is not balanced and is free to move sideways and over the lip of the jar, therefore flowing toward the ground.