What is an ATM deposit hold?

An ATM deposit hold applies to checks that are deposited at the bank's ATM's machine. Given, checks take a few days to clear. If you were to deposit the check in person, the funds would not be available instantly, same exists with ATM deposits. Since the funds do, however, show up as pending transactions, the ATM deposit hold offsets the deposited check which has yet to clear.

Most banks don't hold the full balance of the check. They typically hold the amount of the check less $100. Meaning, upon deposit, you have access to $100 and the rest when the check clears, 3 days later. The $100 is given by the bank in good faith, assuming the check will clear.