Answer: 
A shield volcano is a very large, gently 'sloping mound' composed mainly of 'basaltic lava flows'. 
Step-by-step explanation: 
- The volcanoes are broadly classified into four major types, viz. Cinder Volcanoes, Composite Volcanoes, Lava Domes, and Shield Volcanoes. 
 
- Out of these four, the Shield Volcanoes are the largest in size and span. 
 
- The low viscosity of the lava that comes out of Shield Volcanoes is due to the presence of a high amount of molten basalt in the lava.