The internal angle formed by the junction of two sloping sides of a roof.
Merriam-Webster Online Dictionaryvalley (noun)
a) an elongate depression of the earth's surface usually between ranges of hills or mountains
b) an area drained by a river and its tributaries
a low point or condition
a) - hollow depression
b) the place of meeting of two slopes of a roof that form on the plan a reentrant angle
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A valley is a low area between hills or mountains often with a river running through it. In geology, a valley or dale is a depression that is longer than it is wide. The terms U-shaped and V-shaped are descriptive terms of geography to characterize the form of valleys. Most valleys belong to one of these two main types or a mixture of them, at least with respect to the cross section of the slopes or hillsides.