Pipeline: A line of connected pipes used for carrying liquids or gases over a long distance.
Pressure: The continuous force exerted on one object (like the inside of a pipe) by something in contact with it (like the water inside of it).
PSI: Pounds per square inch. A unit of pressure measured in force (pounds) exerted on a given surface area (square inch). Water flowing through a pipe can create a lot of pressure, and engineers have to have a way to measure that pressure.
Water pressure: A force that affects the rate at which water flows. The greater the pressure, the faster the water flows.