A loch is the name given to a body of water in Scotland; as well as referring to lakes, it is also used for some large fjord-like inlets on the western and northern coasts, known as sea lochs. Although there is no distinct size definition, smaller bodies of water are often known as lochans or lochens.
In Ireland a loch is spelled lough in Hiberno-English, although ironically loch is the spelling used in the Irish language. The Scottish spelling is retained by many in Northern Ireland, where Ulster Scots is spoken more than Irish. The word lough is also used in Northumbria to denote such a body of water, though the pronunciation is different.
Perhaps the most famous Scottish loch is Loch Ness, although there are other large examples such as Loch Shin, Loch Tay and Loch Lomond.
Some new reservoirs for hydroelectric schemes have been given names faithful to the names for natural bodies of water - for example: the Loch Sloy scheme, and Lochs Lagan and Treig (which form part of the Lochaber hydroelectric scheme near Fort William). Other expanses are simply called reservoirs, eg: Blackwater Reservoir above Kinlochleven.
Scotland has exactly one lake, the Lake of Menteith (a corruption of the Scots Laich o Menteith).