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 quick way to clean corrosion off your battery, especially if you are in a place where you don't have tools or time to disconnect the battery from the terminals is to find a can of soda and pour it on the post and terminal where corrosion build up is.