A fluid is a substance which deforms continuously under the action of shearing forces. That is, if a fluid is at rest, there can be no shearing forces acting, and therefore, all forces in the fluid must be perpendicular to the planes upon which they act. Pressure is the measure of a force on a specified area. Depending on the application, there can be many different ways of interpreting pressure: absolute pressure, gauge pressure, vacuum pressure, differential pressure and sealed pressure. Manometer is a device for measuring fluid pressure consisting of a bent tube containing one or more liquid of different specific gravities. Pressure gauge is another device used for the measurement of pressure. This chapter introduces several kinematic concepts related to flowing fluids. Fluid flow can be steady or unsteady, depending on the fluid’s velocity. Velocity is an important basic parameter governing a flow field.