「買い物する」 (kaimono suru) means "to shop" or "to go shopping." It refers to the activity of buying things, such as food, clothes, or other items. It's a common everyday action. You can use it with places like 「デパートで」 (at a department store). For example, 「デパートで買い物します。」 (I will shop at the department store.)

「買(か)い物(もの)する」は、物(もの)を買(か)うことです。デパートで買(か)い物(もの)します。