Zest is a kind of zeal or enthusiasm. If you've got a zest for something, you put your whole heart and soul into it. Dancers who have great zest leap, kick, and soar their way around the stage with a kind of joyful energy.
Oddly enough, zest can also be the outer peel of a lemon or orange, which chefs scrape into their dishes when they want to add some tartness and tanginess to a recipe. People who live with that same kind of spice are said to have a "zest for life." In other words, they live their lives with a lot of flavor and gusto. A student who has a zest for learning dives into her books with an enjoyment and relish most people reserve for their wedding day.