What is Teller?

Legal Definition
An officer in a bank or other institution. He is said to take that name from tallier, or one who kept a tally, because it is his duty to keep the accounts between the bank or other institution and its customers, or to make their accounts tally. In another sense teller signifies a person appointed to receive votes. In England the name of teller is given to certain officers in the exchequer.
-- Bouviers Law Dictionary
Legal Definition
One who numbers or counts. An officer of a bank who receives or pays out money. Also one appointed to count the votes cast in a deliberative or legislative assembly or other meeting. The name was also given to certain officers formerly attached to the English exchequer. The teller is a considerable officer in the exchequer, of which officers there are four, whose office is to receive all money due to the king, and to give the clerk of the pells a bill to charge him therewith. They also pay to all persons any money payable by the king, and make weekly and yearly books of their receipts and payments, which they deliver to the lord treasurer. Cowell; Jacob. See Tellers iu parliament.
-- Black's Law Dictionary
Legal Definition
One appointed to count votes cast.
-- Ballentine's Law Dictionary