The pH scale was designed to measure the acidity or alkalinity of a liquid solution, in the case of a swimming pool, water, or H20.
The actual meaning of the letters p and H in the name of the scale is debatable. The most popular explanation is that pH is stands for potential hydrogen. Others say the P stands for Power, the word power being potenz in German. Others argue the P stands for puissance, power in French, or the Latin pondus.