A coffin is not the same as a casket. A coffin has a slight diamond shape to its design and tapers down from a broad area where the deceased shoulders will be, to a narrow squared bottom where the feet will lay. A casket on the other hand, is a rectangular shape and often built from bulkier, heavier timber. Caskets most often feature a higher quality craftsmanship and might also include higher quality handles and fittings.
It’s also worth mentioning that you can get ashes caskets. These are much smaller boxes or containers which are used as a vessel to contain your loved ones ashes after a cremation.