Demurrage and detention are costs that arise because of poor planning, unforeseen circumstances or bad communication and can often result in thousands of dollars in per diem charges. Even though Demurrage charges play such a huge role in the final costs of shipments, terms are often not understood.
Demurrage & Detention are a matter of allowed free-days, determining the number of days a shipper can use the container for free. If this free time is exceeded, the user has to pay a demurrage & detention charge, usually calculated per day.
The difference between Demurrage and Detention is that Demurrage always relates to the cargo and describes the time while cargo is in the container. Detention relates only to the time a container is empty after unpacking or before loading.
Read more at https://container-xchange.com/blog/demurrage-detention/