Definition
Listing specific deductible expenses on your return, mainly mortgage interest, state and local taxes, charitable gifts, and large medical costs, instead of taking the flat standard deduction. You take whichever is larger; only the amount above the standard deduction produces extra tax savings.
Why it matters
Since the standard deduction roughly doubled in 2018, most filers no longer itemize, which changes old advice: mortgage interest and donations only cut taxes once total itemized deductions beat the flat amount. Bunching two years of donations into one is a common response.