Short answers, pulled from the story.
Pressure equals the amount of force applied perpendicular to an object's surface divided by the unit area over which it spreads. Scientists denote this quantity with the symbol p or P, though the International Union of Pure and Applied Chemistry recommends using a lower-case p.
The name pascal entered official use in 1971 before that scientists expressed it simply as newtons per square metre. The SI unit for pressure is equal to one newton per square metre.
Blaise Pascal and Daniel Bernoulli established the core concepts of fluid pressure. Their work distinguishes between open conditions like oceans and closed systems like pipes.
Water pressure depends directly on depth and density rather than total volume. When a person swims deeper, water pressure acts against their eardrums because pressure rises by approximately one decibar per meter of depth.
Liquid mercury has been observed sustaining up to minus 142 megapascals inside clean glass containers. Bulk solids and liquids sustain negative absolute pressure by pulling on them within metastable states.