A shield volcano is a wide volcano with shallowly-sloping sides.
Shield volcanoes are formed by lava flows of low viscosity - lava that flows easily.
Consequently, a volcanic mountain having a broad profile is built up over time by flow after flow of relatively fluid basaltic lava issuing from vents or fissures on the surface of the volcano.
Many of the largest volcanoes on Earth are shield volcanoes.
The largest is Mauna Loa on the Big Island of Hawaii; all the volcanoes in the Hawaiian Islands are shield volcanoes.
There are also shield volcanoes, for example, in Washington, Oregon, and the Galapagos Islands.
The Piton de la Fournaise, on Reunion Island, is one of the more active shield volcanoes on earth, with one eruption per year on average.