Short answers, pulled from the story.
Pressure is defined as the force applied perpendicular to a surface divided by the area over which that force is distributed. It is a scalar quantity that has magnitude but no direction, distinguishing it from vector forces.
The pascal was officially added to the SI system in 1971 to replace the less specific newton per square metre. One pascal equals one newton per square metre or one kilogram per meter per second squared.
Blaise Pascal discovered Pascal's Law in the 17th century. This principle states that when a liquid is confined, the pressure at any given point is the same in all directions.
The International Union of Pure and Applied Chemistry now recommends 100,000 pascals for the standard atmosphere. Before 1982, the value was often used as 101,325 pascals, creating a subtle divergence in scientific definitions.
Liquid mercury has been observed to sustain up to negative 140 megapascals in clean glass containers. Negative liquid pressures are thought to be involved in the ascent of sap in plants taller than 10 metres.