Something parched is excessively dry and hot, in extreme need of water, like a desert, a neglected plant, or your throat after a five-kilometer run.
Some foods, like corn, beans, or grains, may be parched, or toasted, to bring out their flavor and help preserve them. American Indians parched corn to make it keep and remain edible over the winter. They taught this to the new colonists, and parched corn later became a staple of explorers like Lewis and Clark, as well as soldiers during the Civil War. Laura Ingalls Wilder wrote of parched corn, "It crackled and crunched, and its taste was sweet and brown."