In Scotland

Scotland

Scotland is a country that is part of the United Kingdom. Occupying the northern third of the island of Great Britain, it shares a border with England to the south and is bounded by the North Sea to the east, the Atlantic Ocean to the north and west, and the North Channel and Irish Sea to the...

 and northern England a Linn is a geographical water feature.

In Scotland it describes where a watercourse has cut through a shelf of hard rock creating a narrow (usually), steep-sided cut though which the watercourse runs.

Typically there is only one named Linn on any watercourse - although obviously - there may actually be more than one feature with the necessary attributes.

The photograph of the Linn of Dee illustrates the attributes of a typical 'Linn'.

In Gordon (1925) the author describing a walk down Glen Avon in the Cairngorms

Cairngorms

The Cairngorms are a mountain range in the eastern Highlands of Scotland closely associated with the mountain of the same name - Cairn Gorm.-Name:...

 mentions two Linns on the River Avon - first:

Second:
A linn may also refer to a waterfall or a pool at the foot of a waterfall , with the derivation a confusion of Scots Gaelic linne (pool) and Old English hlynn (torrent).