In the modern Gaelic languages, Lochlann (Irish: [ˈl̪ˠɔxl̪ˠən̪ˠ]) signifies Scandinavia or, more specifically, Norway. As such it is cognate with the Welsh name for Scandinavia, Llychlyn (pronounced [ˈɬəχlɨn]). In both old Gaelic and old Welsh, such names literally mean 'land of lakes' or 'land of swamps'.

It may originally have referred to the mythical, undersea otherworldly abode of the Fomorians of Irish mythology. At times it may have referred to an early Norse settlement in Scotland.

Classical Gaelic literature and other sources from early medieval Ireland first featured the name, in earlier forms like Lothlend and Laithlind. In Irish, the adjectival noun Lochlannach (IPA: [ˈl̪ˠɔxl̪ˠən̪ˠəx], 'person belonging to Lochlann') has an additional sense of 'raider' or, more specifically, a Viking.

All uses of the word Lochlann relate it to Nordic realms of Europe. While the traditional view has identified Laithlind with Norway, some have preferred to locate it in a Norse-dominated part of Scotland, perhaps the Hebrides or the Northern Isles. Donnchadh Ó Corráin states that Laithlinn was the name of Viking Scotland, and that a substantial part of Scotland—the Northern and Western Isles and large areas of the coastal mainland from Caithness and Sutherland to Argyll—was conquered by the Vikings in the first quarter of the ninth century and a Viking kingdom was set up there earlier than the middle of the century.

The Fragmentary Annals of Ireland contain numerous reference to the Lochlanns, who are clearly Vikings and feared and distrusted by the writers. However relatively few named individuals are identified from amongst their number and their relationships with one another are largely obscure.

Jarl Tomrair, described as the "tanist of the king of Lochlann" fell in the Battle of Sciath Nechtain (near modern Castledermot) in 848.

In 851 Zain, also identified as the "half-king of the Lochlanns" and Iargna "the two chiefs of the fleet of the Lochlanns" are recorded as fighting against the Danes in Carlingford Lough. The same source notes that in the sixth year of the reign of Maelsechlainn, circa 852 Amlaíb "the son of the King of Lochlann, came to Erin, and he brought with him commands from his father for many rents and tributes, but he left suddenly. Imhar, his younger brother, came after him to levy the same rents." Amlaíb is also called the "son of the king of Laithlind" by the Annals of Ulster in 853. While certainly of Scandinavian origin – Amlaíb is the Old Irish representation of the Old Norse name Oláfr – the question of Amlaíb's immediate origins is debated. In 871 he "went from Erin to Lochlann to wage war on the Lochlanns" to assist his father Goffridh who had "come for him".

Hona, who the annalists believed was a druid and Tomrir Torra were "two noble chiefs", "of great fame among their own people", and "of the best race of the Lochlanns", although their careers appear to have been otherwise unrecorded. They died whilst fighting the men of Munster in 860.