A ria is a geological term for a normal valley that has been drowned or flooded so that it is now an inlet of the sea. From the Spanish ría 'river-mouth'. (In the news in November 2002, with the rias of Galicia about to be covered in oil from the sunken Prestige).
As an abbreviation, RIA = (1) Royal Irish Academy; (2) Regulatory Impact Analysis.
The character played by Wendy Craig in the bittersweet TV comedy Butterflies was Ria.