A lough is a body of water and is either:
It can also be used as a surname, with various pronunciations: law, loch, low, lowe, loth, loff, lohguh.
Lough is a Hiberno-English form of the Old Irish word loch, which means lake, or bay. The form loch is also used in Irish English, Lough is also used for some small bodies of water in the far north of England.
Except when individually named, loughs are often referred to as lakes, fjords, estuaries, and sea inlets. Thus lake district and estuary bed may be used in preference to lough district and lough bed. (This practice is not followed to anything like the same degree in English use of loch.)
Irish loughs 
Almost all lakes in Ireland are named loughs in their anglicised form. Lough Neagh in Northern Ireland is the largest lake in the British Isles. The three on the River Shannon are Lough Allen, Lough Ree, and Lough Derg. Upper and Lower Lough Erne are two consecutive lakes in Fermanagh, an area often referred to as Ireland's lake district.
English loughs 
In the north of England, lough survives in the names of some bodies of water and other place names. Many of these formed in the low ground to the north of the Whin Sill escarpment upon which part of Hadrian's Wall runs.
See also 
|Look up lough in Wiktionary, the free dictionary.|
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|Look up loch in Wiktionary, the free dictionary.|