A more thorough explanation:

Definition: The state of being behind in the payment of a debt or the discharge of an obligation. It can also refer to an unpaid or overdue debt or an unfinished duty.

Examples:

• The tenant was in arrears with the rent payment.
• The company was in arrears with their taxes.
• The student was in arrears with their homework assignments.

These examples illustrate how arrear refers to being behind in fulfilling a responsibility or obligation. In the first example, the tenant has not paid their rent on time and is therefore in arrears. In the second example, the company has not paid their taxes on time and is also in arrears. In the third example, the student has not completed their homework assignments on time and is in arrears with their work.