What is a debit in accounting, and which option best describes it?

The correct option is the first one.

In accounting, a debit is an entry made on the left-hand side of a T-account. It typically increases asset and expense accounts, and decreases liability, equity, and revenue accounts.

• An entry recording a sum owed, listed on the left-hand side or column of an account - This accurately describes a debit. For example, when a customer owes money to a business (creating an Accounts Receivable), the Accounts Receivable account (an asset) is debited, which is an increase on the left-hand side. Similarly, when a business pays off a liability (a sum owed by the business), the liability account decreases, which is also recorded as a debit.

The final answer is $\boxed{\text{An entry recording a sum owed, listed on the left-hand side or column of an account}}$