Definitions for lactic acid
Random House Webster's College Dictionary
a syrupy liquid, C3H6O3, produced by anaerobic metabolism, as in the fermentation of milk or carbohydrates.
Origin of lactic acid:
a clear odorless hygroscopic syrupy carboxylic acid found in sour milk and in many fruits
2-hydroxy-propanoic acid (CH.CHOH.COH), a syrupy liquid, soluble in water; found in milk, wine and many fruits; used as a food additive and in many industrial applications.
U.S. National Library of Medicine
A normal intermediate in the fermentation (oxidation, metabolism) of sugar. The concentrated form is used internally to prevent gastrointestinal fermentation. (From Stedman, 26th ed)