As nouns the difference between rea and ria

is that rea is alternative form of lang=en while ria is a submergent coastal landform, often known as a drowned river valley.

As initialisms the difference between rea and ria

is that rea is request for an equitable adjustment, a term used in contracting with government entities in the United States to indicate that compensation is sought for unexpected costs arising in the fulfillment of a contract while RIA is initialism of Rich Internet Application or "Rich Internet Application"|lang=en.