Final answer:
An atoll is a type of reef that is characterized by having a lagoon.
Step-by-step explanation:
A type of reef characterized by having a lagoon is called an atoll. Atolls are circular or horseshoe-shaped reefs that surround a lagoon. They are formed from coral reefs that grow on the rim of volcanic islands, and as the island erodes, the coral reef remains, forming the atoll.
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