What is a bank account held by one person as custodian for another?
It usually means that an adult has opened an account for a child
and has the ability to add/subtract or "control" the account for
the child. Can also be for adults; ex-when a large amount of money
is involved and custodian wants to limit beneficiary's access.
Basically, someone besides the account holder who has access to and
can change said account.