It means to AGREE. ✔
Let's say that you have a checking account that you have labeled, "Checking (1234)."
You receive your bank statement on the 5th of every month.
On the statement, you find the ending balance (or "new balance").
In QuickBooks Online, you go to the Gear, then to Reconcile.
In QuickBooks Desktop, you go to the Banking menu, then to Reconcile.
In the Reconcile window, you choose Checking (1234).
Then you enter the ending balance from the bank statement and the ending date.
The first thing you do in the Reconciliation Window is to make sure that the beginning balance in QuickBooks AGREES with the beginning balance on the bank statement.
Next, you check off all the deposits and credits in QuickBooks that match the deposits and credits in the bank statement.
If QuickBooks and the Bank AGREE on the deposits, then you have "reconciled" the deposits for the month.
After that, you check off the checks and payments in the same way, and if they AGREE, you have "reconciled" the checks and payments for the month.
If you are in total AGREEMENT, you will see a difference of zero, and you have the "green light" that you can Reconcile now.