Illustrated Glossary of Organic Chemistry

pH: The negative log of the hydronium ion concentration; pH = -log[H3O+]. A measure of aqueous solution acidity or basicity.

Car battery (aqueous sulfuric acid)
pH = 0 - 1
Strongly acidic
Vinegar (aqueous acetic acid)
pH = 4 - 5
Weakly acidic
pH = 7
Egg whites
pH = 8
Weakly basic
Drain cleaner (aqueous NaOH)
pH = 14
Strongly basic
Approximate pH of some household items.