The word "due" primarily refers to something that is expected or owed at a particular time. It can imply that an obligation exists, such as a payment that is required by a deadline or something that is rightfully expected as part of a process or arrangement.
The word "due" comes from the Old French word "deu," which is derived from the Latin "debet," meaning "he owes." The original sense relates to obligation or something owed, which has evolved over time in usage.