Step 1: Understanding Bank.
A bank is a financial institution that accepts deposits, provides loans, and performs other financial services. It is not an individual or society in itself.
Step 2: Analyzing the options.
(A) A person – Incorrect, a bank is not a single person.
(B) An institution – Correct, a bank is a financial institution.
(C) A society – Incorrect, although some banks may be cooperative societies, in general a bank is not defined as one.
(D) All of these – Incorrect, as the precise definition is institution.
Step 3: Conclusion.
Thus, the correct answer is that a bank is an institution.