sumo match held in front of the Emperor
A special sumo event performed for the imperial family; historically significant and ceremonial.
During the Edo period, sumo matches in front of the Emperor were often held.
Similar meaning, but 天覧相撲 specifically refers to a sumo match viewed by the Emperor, while 上覧相撲 can also refer to viewing by the shogun or other high-ranking nobles.
From 上覧 (imperial inspection) and 相撲 (sumo).