PH

The PH formula is given as PH=-log(H+). The H+ is the number of free ions of hydrogen. A seven PH is considered neutral. Discuss what having a low PH and a high PH means. What does a 12 PH mean? How about a 2? Which is more caustic? Is either a good thing at extremely high or low values? Explain fully as to what a PH means to you and what you use it for.