The vast majority of the inscriptions consist of personal names.
According to the High Medieval Bríatharogam, the letters are named after various trees. For this reason, Ogham is sometimes known as the Celtic tree alphabet.
The etymology of the word ogam or ogham remains unclear. One possible origin is from the Irish og-úaim 'point-seam', referring to the seam made by the point of a sharp weapon.[9]
^Thurneysen, R. A Grammar of Old Irish page 9: "Older as a rule even than the above archaic material are the sepulchral inscriptions in a special alphabet called ogom or ogum in Middle Irish, ogham in Modern Irish."
^McManus (1991) is aware of a total of 382 orthodox inscriptions. The later scholastic inscriptions have no definite endpoint and continue into the Middle Irish and even Modern Irish periods, and record also names in other languages, such as Old Norse, (Old) Welsh, Latin and possibly Pictish.
See Forsyth, K.; "Abstract: The Three Writing Systems of the Picts." in Black et al. Celtic Connections: Proceedings of the Tenth International Congress of Celtic Studies, Vol. 1. East Linton: Tuckwell Press (1999), p. 508; Richard A. V. Cox, The Language of the Ogam Inscriptions of Scotland, Dept. of Celtic, Aberdeen University ISBN0-9523911-3-9[1];
See also The New Companion to the Literature of Wales, by Meic Stephens, p. 540.
^O'Kelly, Michael J., Early Ireland, an Introduction to Irish Prehistory, p. 251, Cambridge University Press, 1989