(1) (chemistry) The measure of the hydrogen ion concentration of a solution.
(2) (chemistry) A measure to determine the acidity or alkalinity of a substance.
(3) (chemistry) The negative logarithm of hydrogen ion concentration expressed in molarity.
(4) (metrology) Symbol for picohenry.
In chemistry, the pH of different cellular compartments, body fluids, and organs is usually tightly regulated in a process called acid-base homeostasis.
Word origin: p, denoting negative logarithm, and H, denoting hydrogen.