Ben Lugmore (Irish: Binn Log Mhór, meaning 'peak of the big hollow') at 803 metres (2,635 ft) is the 29th-highest peak in Ireland on the Arderin scale, and the 37th-highest peak on the Vandeleur-Lynam scale. It is in a horseshoe-shaped massif that includes the slightly higher peak of Mweelrea at 814 metres (2,671 ft), the highest mountain in the Irish province of Connacht. The massif is between Killary Harbour and Doo Lough, in County Mayo.

The peak is noted for its long summit ridge that forms a deep cliff-lined headwall around the corrie of Lug More (Irish: Coum Dubh); the corrie includes a feature known as The Ramp that climbers use to access the summit ridge, as well as rock climbs and winter ice climbs. While the peak can be accessed via a 3-hour walk from the corrie below, it is also summited by way of the 6-7 hour Mweelrea Horseshoe, described as a "top three" mountain walk in Ireland.

Irish academic Paul Tempan lists Ben Lugmore as an anglicisation of the Irish: Binn Log Mhór that translates as "peak of the big hollow", and which describes the deep corrie on Lugmore's northeast face called Lug More (split into two words). Patrick Weston Joyce chronicled that the term Lugmore, which he translated as "Great Hollow", appears in several other Irish placenames; and there are several entries in the Placenames Database of Ireland.

Ben Lugmore's geology is what is known as the Mweelrea Formation, and is very different from that of the Twelve Bens, on the other side of Killary Harbour. At a summary level, the Mweelrea Formation consists of Ordovician period sandstones originally deposited on large alluvial fans, and distally-equivalent alluvial plains and delta fans. Interbedded with these sandstones are tufts, being ash deposits from Ordovician period volcanos.

The peak of Ben Lugmore lies on the northern arm of the horseshoe that forms the massif of the Mweelrea Mountains, which is bounded by Killary Harbour, Ireland's deepest fjord, to the south, and Doo Lough to the north; Mweelrea, the provincial top for Connacht, lies near the apex of this horseshoe.

Ben Lugmore is described as having a small sharp "airy" summit which lies on a high narrow southeast to northwest ridge that links with Ben Bury, and then on to Mweelrea. This ridge includes two high subsidiary summits either side of Ben Lugmore, both of which are of equal height: Ben Lugmore West Top at 790 metres (2,590 ft), whose prominence of 47 metres (154 ft) qualifies it as a Vandeleur-Lynam and a Hewitt, and Ben Lugmore East Top at 790 metres (2,590 ft), whose prominence of 37 metres (121 ft) also qualifies it as a Vandeleur-Lynam and a Hewitt. From a distance, Ben Lugmore's profile is that of a long and high sharp ridge, along which its various summits (main and subsidiary) are dotted.

Northeast of Ben Lugmore's ridge are the cliffs of the deep corrie of Lug More (also called Irish: Coum Dubh), which itself looks into the small valley of Glencullin at the junction of Doo Lough and Glencullin Lough. To the southwest of the ridge is the valley of Glenconnelly; and where the high southwestern cliffs of Ben Lugmore West Top, Benbury and Mweelrea circle the northern corrie lake at the head of the Glenconnelly valley, known as Lough Bellawaum.

Ben Lugmore's own prominence of 158 metres (518 ft) qualifies it as a Marilyn, and it also ranks it as the 18th-highest mountain in Ireland on the MountainViews Online Database 100 Highest Irish Mountains, where the minimum prominence threshold is 100 metres. The peak is listed as the 29th-highest peak in Ireland on the Arderin scale, and the 37th-highest peak on the Vandeleur-Lynam scale.