군것질 is regarded same as 간식 but usually snacks or junk food rather than fruits. something bad for your health then it is 군것질, otherwise, 간식:) 과일 = fruits that you usually eat. 열매 = any fruits from trees whether eatable or not. fruits shop is 과일 가게, never 열매 가게 because you don't sell fruits not eatable in fruits shop.