hydrostatic pressure
Hydrostatic pressure is the pressure inside a fluid that is sitting still, caused simply by the weight of the fluid stacked above. Dive to the bottom of a swimming pool and you feel it press on your ears; the deeper you go, the more it squeezes. It answers a clear question: in a liquid at rest, how does the pressure change as you go down?
The precise rule is that the pressure rises steadily with depth. If the pressure at the top surface is P_0, then at a depth h below that surface the pressure is P = P_0 + rho g h, where rho is the fluid's density, g is the acceleration due to gravity (about 9.8 m/s^2), and h is the depth. The extra term rho g h is exactly the weight of a column of fluid of height h pressing down on each unit of area. A striking consequence is that the pressure depends only on the depth, not on the shape of the container or how much fluid there is in total.
This is why dam walls are built thick at the bottom, where the water pushes hardest, and why deep-sea creatures must withstand crushing pressures. One honest subtlety, sometimes called the hydrostatic paradox: a narrow tube and a wide lake filled to the same depth have the same pressure at the bottom. It is the height of the fluid above a point that sets the pressure, never the total weight of fluid in the vessel.
At 10 m down in fresh water the added pressure is rho g h = 1000 × 9.8 × 10 ≈ 98 000 Pa, roughly one extra atmosphere. So a diver 10 m down feels about twice the pressure they felt at the surface.
Pressure grows with depth as P = P_0 + rho g h, set by how far down you are, not by the container's shape.
Hydrostatic pressure depends only on depth (and the fluid's density), not on the shape of the vessel or the total amount of fluid, the hydrostatic paradox.