What type of coral formation runs parallel to the shore and is separated from it by a lagoon?

A barrier reef is a type of coral formation that runs parallel to the shore and is separated from it by a lagoon. These reefs are usually located further out from the coastline than fringing reefs and provide a significant barrier against wave action and storms. The lagoon created between the barrier reef and the shore is typically shallow and can be a rich habitat for various marine life.

Fringing reefs, on the other hand, are directly adjacent to the coastline and do not have a significant lagoon separating them from the shore. Atolls are ring-shaped coral reefs that generally encircle a lagoon but are found in deeper oceanic regions, not close to a continental shore. Patch reefs are small, isolated reefs that can be found within lagoons but do not form a continuous line parallel to the coastline like barrier reefs do. Thus, the defining characteristics of a barrier reef are precisely what makes it the correct answer in this context.