The name "Persia" was used internationally for centuries to refer to the country and its people, but it was officially changed to "Iran" in 1935 by the reigning Shah, Reza Shah Pahlavi. The change was intended to emphasize the country's Iranian identity and to shed the historical association with the Achaemenid Persian Empire.
While "Persia" is no longer officially used, it's still sometimes used in historical contexts or by individuals who prefer to use the older term.