What does federal refund means

It means the amount of money that the IRS owes you once you file your tax return.

After you fill out your 1040 federal tax return and enter all your W2s and any 1099s you will either have a Refund or have a tax due.  Tax Due means you owe more to the IRS.  A Refund means you overpaid during the year and the IRS will give you money back, either with a check or a Direct Deposit to your bank account.