Belfalas was a region of southern Gondor.
Belfalas, or Great Shore or Cost of the Powers (bel = powers; falas = cost), formed a part of Dor-en-Ernil, or the "Prince's land". The Prince in question here was the Lord of Dol Amroth, who lived at the city bearing his name.
At the start of the second millennium of the Third Age, a certain Imrazôr the Númenórean lived in and ruled over the Belfalas. He married Mithrellas, a Silvan Elf of Lórien, and their son Galador became the first Prince of Dol Amroth.
South of the Belfalas lay a great Bay, which was named after it the Bay of Belfalas.
During the War of the Ring, the Belfalas was raided by the Corsairs of Umbar, and therefore did not send any men to help defend Minas Tirith, until Aragorn liberated the coast with the Grey Company, freeing Gondor's southern armies to follow him north to relieve Minas Tirith.