Blood pressure is usually expressed in terms of the systolic pressure (maximum during one heart beat) pressure over diastolic pressure (minimum in between two heart beats) and is measured in millimeters of mercury (mmHg), above the surrounding atmospheric pressure (considered to be zero for convenience).
Corrosion on the terminals is due to hydrogen gas being released from the acid in the battery. It mixes with other things in the atmosphere under the hood and produces the corrosion you see on the terminals. Generally, if the corrosion is occurring on the negative terminal, your system is probably undercharging.
The process is cyclic until perforation of the component occurs. Erosion-corrosion is usually found at high flow rates around tube blockages, tube inlet ends, or in pump impellers. The photo shows erosion corrosion of a cast aluminum pump casing due to excessively high flow rate of the coolant. Cavitation-corrosion is a special form of erosion-corrosion. It is caused by water bubbles produced by a high-speed impeller, which then collapse and cause pits on the metal surface.