In a narrow sense, the name refers to the range of Old Red Sandstone peaks which lie to the south of Brecon. Sometimes referred to as “the central Beacons” they include South Wales’ highest mountain, Pen y Fan. The range forms the central section of the Brecon Beacons National Park (Parc Cenedlaethol Bannau Brycheiniog), a designation which also encompasses ranges both to the east and the west of “the central Beacons”. This much wider area is also commonly referred to as “the Brecon Beacons”, and it includes the Black Mountains to the east as well as the similarly named but quite distinct Black Mountain to the west. The highest peaks include Fan Brycheiniog to the west and Pen y Fan in the central part. They share the same basic geology as the central range, and so exhibit many similar features, such the north-facing escarpment and glacial features such as lakes and cwms below the escarpment. They all fall within the border of the national park. Read more here and visiting information here