Unlike with many other landforms, there is no universally accepted definition of a mountain. Many geographers state that a mountain is greater than 300 metres (1,000 feet) above sea level. Other definitions, such as the one in the Oxford English Dictionary, put the hill limit at twice that. Still others make distinctions about the degree of slope (including two degrees or five degrees). In Scotland, meanwhile, landforms with distinct summits are called ‘hills’ no matter what their height. But in America, there are several ‘mounts’ that are less than 300 metres (1,000 feet) tall. So, essentially, a hill becomes a mountain when someone names it as such.
Answered by Shanna Freeman, How It Works contributor.