Something is refreshing if it reinvigorates you, or seems new and exciting. The offer of a refreshing glass of iced tea would be especially refreshing if it came from your normally cranky sister.
Mint toothpaste is refreshing — clean and brisk — and a cool ocean breeze is refreshing on a hot day. If you're used to seeing wilted salads and pale lasagna in your school cafeteria every day, a refreshing change would be a taco bar or homemade pizza. Refreshing comes from the verb refresh, which has a Germanic root similar to frisc, "fresh" in Old High German.