Translation according to P. W. Joyce:
Back, which appears in a few names, often represents the Irish Bate [back], a bend or crook. There is a townland called Back in Galway, another in Derry, and a double townland same name in Tyrone. Backaderry, near Drumgooland in Down, the bend of the derry or oakwood. There was an ancient territory in Tirawley in Mayo called An-da-Bac, "The Two Bacs," which anglicised name is now applied to a district between the river Moy and Lough Conn. But observe that in many or most cases " Back," when it occurs in local names is merely the English word "back," as in "Back of the hill," near Ardagh in Longford.