🎓 pH is a measure of the acidity or basicity of a solution. It is defined as the negative logarithm of the concentration of hydrogen ions (H+) in the solution. pH ranges from 0 to 14, with a pH of 7 being neutral, a pH less than 7 being acidic, and a pH greater than 7 being basic. A change of one pH unit represents a ten-fold change in the concentration of H+.