A lump sum payment is a  single, large payment made to an employee, rather than smaller, incremental payments. 

For example, an employee taking a month of annual leave may be paid the entire month of wages in one transfer, rather than weekly; this is not very common in smaller organizations due to the lack of financial means; however bigger organizations practice this more frequently, some of the reasons of a lump sum payment may include taking care of a sick parent or child, or grieving the death of a loved one.