According to the most popular theory, the name of the country of Peru comes from the local word "biru," which means river.

An excerpt from the article 43 facts about Peru

According to another theory, the name of the country may come from the name of the local ruler Biru, who lived near San Miguel Bay in Panama at the beginning of the 16th century. The Spanish conquistadors considered it to be the southernmost part of the New World. When Francisco Pizarro invaded areas further south, he named them Biru or Peru.

However, the then writer Inca Garcilaso de la Vega, the son of an Inca princess and a conquistador, wrote that Biru was the name of a common Indian encountered by the crew of a Spanish ship, and when asked about the name of the country, he gave his name. Yet another hypothesis assumes that the name of the country may come from the word Pelu, which was the former local name of the region.