An itemized deduction is a specific expense that taxpayers can list on their tax return to reduce their taxable income. Instead of taking the standard deduction, individuals can choose to itemize deductions for expenses such as mortgage interest, medical expenses, and charitable contributions. This can lead to a lower tax bill if the total of these expenses exceeds the standard deduction amount. To claim itemized deductions, taxpayers must complete Schedule A of the IRS Form 1040. It's important to keep accurate records and receipts for all eligible expenses, as the Internal Revenue Service may require documentation to verify the deductions claimed.