what does o stand for in irish names
Irish name A first name may be modified by an adjective to distinguish its bearer from other people with the same name. Mór ("big") and Óg ("young") are used to distinguish father and son, like English "junior" and "senior", but are placed between the given name and the surname: Seán Óg Ó Súilleabháin corresponds to "John O'Sullivan Jr." (although anglicised versions of the name often drop the "O'" from the name).
Orr (surname) Orr is a surname common throughout the English-speaking world, but especially in Scotland, Ulster, the United States, Canada, and northern England. The name is considered to have numerous origins: such as being derived from an Old Norse byname; a Gaelic nickname; and an Old English topographical name, or similar place-name.