Malcolm Noonan (Carlow-Kilkenny, Green Party) | Oireachtas source

That is just one of the accepted definitions. Section 15 states:

“settlement” means a village, town or city identified by the Central Statistics Office in its ‘Alphabetical List of Towns’, or such equivalent document issued by the Central Statistics Office, containing a minimum of 50 occupied dwellings with a maximum distance between any dwelling and the building closest to it of 100 metres.