What does OG mean in Irish names?

What does OG mean in Irish names? Mór (“big”) and Óg (“young”) are used to distinguish father and son, like English “senior” and “junior”, 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).

Mór (“big”) and Óg (“young”) are used to distinguish father and son, like English “senior” and “junior”, 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).