Something that's zesty is fun and exciting. The zesty crowd that attends your party is lively, enthusiastic, and maybe even a little bit loud.
People and parties can both be described as zesty, but you can also talk specifically about food that tastes zesty. When you eat a zesty lunch, it's highly flavored or even spicy. If you give her the extra hot salsa, your mom might say, "Ooh, these enchiladas are zesty!" The adjective comes from zest, the word for the outer part of an orange or lemon peel, which is often added to recipes for extra flavor.