Custodial accounts are those that the bank is holding for the person and depository accounts are those that the bank must be responsible for (savings and checking accounts.
A "custodial account" is an arrangement for holding a financial instrument, contract, or investment (including corporate stock, a note, bond, debenture or other evidence of indebtedness, a currency or commodity transaction, a credit default swap, a swap based upon a nonfinancial index, a notional principal contract (as defined in §1.446-3(c)), an insurance or annuity contract, and any option or other derivative instrument) for the benefit of another person. Reg. §1.1471-5(b)(3)(ii).