SALT is State And Local Tax.  Which includes property tax, any state tax paid like for last year’s return and includes any state withholding from your W2s and any 1099s you have. And any taxes in W2 box 14 and 19 like SDI or VDI. You can only deduct up to 10,000 (5,000 MFS) for SALT State and Local Taxes.

So the amount over 10,000 shows up as a negative number.  It doesn’t mean anything and doesn’t go anywhere.  Just for your info to let you know how much you can’t deduct this year.  There was no limit for 2017 and earlier.