For 2018 taxes, it could very well be the $10,000 State and local tax limit (SALT) that was placed on your tax Deductions by congress.
That SALT limit includes any "income" taxes paid to your state/city/county, PLUS any property taxes you paid. So you may have been close to the limit when you entered your W-2 forms, (and maybe quarterly estimated taxes if you paid those too), and by the time you got to your property taxes, only a portion of them was used before you hit the $10,000 allowed limit.
____________*Answers are correct to the best of my knowledge when posted, but should not be considered to be legal or official tax advice.*
