pH stands for the power of hydrogen, which is a measure of hydrogen ion concentration. The pH scale ranges from 1-14 used to measure how acidic or alkaline a substance is. A pH of 7 is neutral. A pH less than 7 is acidic, and a pH greater than 7 is alkaline. If you were curious, it was invented by Danish chemist S.P.L. Sørensen back in 1909.