The Amounts applied from prior year refunds includes any refund that you chose not to actually receive, but instead you indicated on the tax return for the IRS to keep your refund and apply it toward estimated payments for the following tax year. This has to be a specific choice that you made when you filed the previous year return.
Excess Social Security is a rare occurrence when you have multiple jobs and between the two jobs your income reached the maximum limit for Social Security taxes and you had more than $8239.80 withheld for Social Security tax. When that happens, the excess is added to your other tax payments.
