Abbreviation of Potential Hydrogene ; it means acidity or basicity of a solution and it is defined by water dissociation in ions H+ and OH-.( H+) concentration x (OH-) concentration is a constant ( 10 14 ) in chemistry, this product is expressed as pH = log (H+) .The pH numbers range from 0 to 14, 7 being neutral, and are indices of the acidity (below 7) or alkalinity (above 7).