To make a raisin, you dehydrate a grape. To dehydrate is to remove all of the water from, or to dry up.
When you exercise a lot, it's good to drink water so that your body doesn't dehydrate. Signs of dehydration in a person? Dry mouth, exhaustion, dark urine, the chills, and head rushes. If you experience these, get a drink quick! Signs of dehydration in a fruit? Wrinkled skin and extra sweetness. Yum!