Checkbook
  
A blast from the past...checkbooks are little books or folders that hold checks, which are paper promissory notes that people can write out. Yes, written on the skin of dead trees. Paper. Checks were the ancient method of paying for things without cash. Before Paypal, before credit cards got super easy to get and to use, people used checks.
Checks are linked to bank accounts and when cashed, the amount is withdrawn from the account. The idea is similar to a debit card (actually debit cards are more modern versions of checks, but we'll deal with this looking backward in time), but it takes longer to process and involves paper.
In the old days, before the banks did all the math for you online, you had to "balance" your checkbook. Balancing the checkbook was the process of subtracting all the written checks or other debits, and adding all the deposits, into the account balance. Yes, you did it by hand, writing numbers and doing math using a pen or pencil in a little book of lined paper included in the checkbook.