A groin, often at the end of a littoral cell or at the updrift side of an inlet, intended to prevent sediment passage into the channel beyond. As with other shoreline structures there are often unintended consequences, primarily downdrift erosion on adjacent beaches. Terminal groins are typically used as part of a beach fill program to help contain the placed sand and reduce erosional loss.
The State of North Carolina recently passed legislation that would allow the use of terminal groins despite the state's long standing ban on hardened shoreline structures. See more discussion on the history of this issue and the legislation here.