Full meaning of pH

Mathematically, pH is defined as the negative base-10 logarithm of the hydrogen ion concentration ($\text{H}^+$), expressed in moles per liter ($\text{mol/L}$):

$$\text{pH} = -\log_{10}[\text{H}^+]$$

This logarithmic scale allows for a wide range of hydrogen ion concentrations to be expressed in a compact way.