Answer:
a. NSF check ⇒ non-sufficient funds check: it is a debit memo that decreases the account balance. One or more of the checks from third parties that you deposited didn't have enough funds to be cashed.
b. EFT deposit ⇒ electronic funds transfer: credit memo that increases the account balance. Someone deposited money to your account through an electronic transfer, e.g. online transfer.
c. Service charge ⇒ debit memo that decreases the account balance. This is a fee charged to you by the bank for the banking services provided.
d. Bank correction of an error from recording a $300 check as $30 ⇒ debit memo that decreases account balance. A check that you wrote was erroneously recorded as $30 when its value was $300.