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. 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.