Definition - What does Lost Days mean?
Lost days refer to the total number of work days that are lost (usually scheduled days) as a result of a worker injury or illness. Lost days can also be defined as the number of work days following an injury or illness during which the employee was unable to perform routine functions. Days lost excludes the day of the incident, planned leave, weekends, scheduled vacation days and public holidays.
Safeopedia explains Lost Days
Workplace incidents are common and inevitable. Some injuries are minor and some are major. Major injuries often mean time off work. This time period in which the employee is not available for work but is still an employee is called lost days. These days represent a cost to employers, who must often find a replacement or suffer a loss of efficiency during this time.