The Reiwa era (令和時代 Reiwa jidai, lit. "Age of Sacred Peace") is the official name of the present era of Japanese history, which began on May 1, 2019 following the abdication of Emperor Akihito and the ascension of Crown Prince Naruhito to the Chrysanthemum Throne.
The Reiwa era follows the Heisei era (1989-2019), the Shouwa era (1926-1989), the Taishou era (1912-1926), and the Meiji era (1868-1912). Since the Meiji era, each era has corresponded to the rule of one emperor.
The name of the new era was announced during a press conference in which Chief Cabinet Secretary Suga Yoshihide held up a sign revealing the new name. This event has revived a minor meme, with many posts parodying the reveal of the new name in a fashion that had been done periodically with Suga's predecessor, Obuchi Keizou.