Zeal is dedication or enthusiasm for something. If you have zeal, you're willing, energized, and motivated.
Zeal is often used in a religious sense, meaning devotion to God or another religious cause, like being a missionary. Zeal doesn't have to be religious, though: a feeling of gusto and enthusiasm for anything can be called zeal. People have zeal for sports teams, bands, causes, and (often, but not always) their jobs. If you have passion for something, you have zeal, which is kind of a mix of eagerness and energy and devotion.