Someone who's choosy is very particular or picky. If you're choosy about your food, you might refuse to eat at McDonald's no matter how hungry you are.
Choosy people often have a reputation for being hard to please — they might take a long time to make a decision, or reject several choices as not being quite right. If you're choosy, you might hold out for the very best of something. An old TV commercial for peanut butter included the line, "Choosy moms choose Jif!" Choosy is an American English word, from choose, from the Old English root ceosan, "choose," and also "accept or approve."