Dehydrated garlic flakes (sometimes referred to as instant garlic) are slices or bits of garlic that must be reconstituted before using (unless added to a liquid-based dish, such as soup or stew). When dehydrated garlic flakes are ground, the result is garlic powder. Garlic salt is garlic powder blended with salt and a moisture-absorbing agent.
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.