Sentence:  If you elect to use the Standard Deduction or the Tax Table , and later find you should have itemized your <WSD>deductions</WSD> , you may do so by filing an amended return within the time prescribed for filing a claim for refund . 
Meaning of the word marked with <WSD> tags:  a reduction in the gross amount on which a tax is calculated; reduces taxes by the percentage fixed for the taxpayer's income bracket