Well known in the British Isles, Brittany in France, and perhaps the Almendres Cromlech in Portugal. Chromlech are ancient monuments associated with with prehistoric or neolithic cultures. They can be found in various parts of the world. In Asia, Europe, and Africa. Megalithic construction. Made of large stone blocks.

The word comes from Welsh. Crom (bent); and, llech (slate)
In english, often applying to two different forms. Like an Altar tomb. Or, what is referred to as stone circles, rings or dolmens. Some consisting of a few standing stones in a circular pattern. Others more elaborate. That may include a central burial chamber, or features.

The term is more commonly used in the British Isles.
In and around other regions. Similar structures may be called dolmens, stone circles or rings. Cornish antiquitarian William Borlase begin using the term. When generally describing altar tombs, or dolmens. Prior to Théophile Corret de la Tour d’Auvergne’s published use of Dolmin. In Origines gauloises (1796). It was the 1760s. When, William Borlase begin using the term cromlech. And, with the use of explosives. More and more megalithic structures were uncovered. Being described and published on.

Bibliography: Aubrey Burl: A Guide to the Stone Circles of Britain, Ireland and Brittany. Yale University Press, New Haven 2006, ISBN 0-300-11406-0

“Definition of CROMLECH” (https://www.merriam-webster.com/dictionary/cromlech).
http://www.merriam-webster.com.