mountain boardˈmountain ˌboard (also all-terrain board) noun [countable] 
a long wide board made of plastic or wood, with four rubber wheels, which people use to travel down the sides of mountains for sport—mountain boarding noun [uncountable]—mountain boarder noun [countable]
a long wide board made of plastic or wood, with four rubber wheels, which people use to travel down the sides of mountains for sport—mountain boarding noun [uncountable]—mountain boarder noun [countable]