1. The word "lactic" is an adjective for things relating to or derived from milk. 2. Lactic acid is a bitter-tasting acid that forms when certain bacteria combine with lactose (milk sugar). It's used to impart a tart flavor, as well as in the preservation of some foods. Lactic acid occurs naturally in the souring of milk and can be found in foods such as cheese and yogurt. It's also used in the production of acid-fermented foods such as pickles and sauerkraut.
From The Food Lover's Companion, Fourth edition by Sharon Tyler Herbst and Ron Herbst. Copyright © 2007, 2001, 1995, 1990 by Barron's Educational Series, Inc.