To itemize means to list things one by one, writing down each separate item instead of lumping them together. When you itemize your school supplies for a shopping trip, you don't just write “stuff for school.” Instead, you write: three notebooks, one pack of pencils, two folders, one ruler, and so on.

The word comes from breaking something down into its individual items. If your teacher asks you to itemize the reasons you enjoyed a book, you'd list each reason separately: the exciting plot, the funny main character, the surprising ending. This is more detailed and useful than just saying, “I liked lots of things about it.”

People often itemize expenses, which means listing exactly what they spent money on rather than just giving a total. A business might itemize a bill to show customers: $50 for materials, $30 for labor, $5 for delivery. An itemized receipt shows every purchase separately instead of just the final amount.

The opposite of itemizing would be summarizing or grouping things together. Itemizing takes more time and effort, but it gives you and others a much clearer picture of what you're dealing with.