A dome is a building or roof that usually looks like the upper half of a sphere.
As a roof feature, domes make many religious and government buildings stand out, because if someone is speaking to others inside or under a dome, the voice sounds louder. Also a dome makes it easier to identify an important building, for example a temple or a palace.
A large stadium with a roof over the playing field is often called a "dome". One example of that usage is the Metrodome.
St. Peter's basilica in Vatican City, with a dome, seen from outside.
Golden dome above the mausoleum of Fatima Masumah in Qom
Gilded onion domes of the Cathedral of the Annunciation, Moscow Kremlin
Fiberglass dome cottage in Davis, California. This dome was built in 1972 and is part of the Baggin's End student housing cooperative.
The dome of the United States Capitol in Washington, D.C.