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The Gàidhealtachd ([kɛːəlˠ̪t̪əxk] listen (help·info), English: Gaeldom), sometimes known as A' Ghàidhealtachd (English: the Gàidhealtachd), usually refers to the Scottish highlands and islands, and especially the Scottish Gaelic culture of the area. The corresponding Irish word Gaeltacht however refers strictly to an Irish-speaking area. The term is also used to apply to the Gaelic-speaking areas of Nova Scotia, Canada.
The term the Gàidhealtachd is not truly interchangeable with the term highlands, as it refers to the language and not to the geography. Also, many parts of the highlands no longer have substantial Gaelic-speaking populations, and some parts of what is now thought of as the Highlands have long been Scots-speaking or English speaking areas: Caithness, Cromarty, Grantown-on-Spey, Campbeltown etc. Conversely, several Gaelic-speaking communities lie outwith the Highland, Argyll and Bute and Western Isles council areas, for example Arran and parts of Perth and Kinross. For this reason, the Gàidhealtachd also increasingly refers to the regions in Scotland where Scottish Gaelic is spoken as a native language by much of the population; it can also refer to areas of Nova Scotia and other communities in Canada, such as Glengarry County, Ontario, where the language has historically been spoken.
Until a few centuries ago, the Gàidhealtachd would have included much of modern-day Scotland north of the Firth of Forth and Galloway (up until the 18th century, and maybe later), excepting the Northern Isles, as evidenced by the prevalence of Gaelic-derived place names throughout most of Scotland and contemporary accounts. These include Dundee from the Gaelic Dùn Deagh, Inverness from Inbhir Nis, Argyll from Earra-Ghàidheal, Galloway from Gall-Ghaidhealaibh, and possibly Stirling from Sruighlea (though the etymology is uncertain; see article). Gaelic speakers from what would be considered traditionally English-speaking/non-Gaelic regions today included George Buchanan from Stirlingshire, and Robert the Bruce and Margaret McMurray from Galloway and Ayrshire.
For historical reasons, including the influence of a Scots-speaking royal court in Edinburgh and the plantation of merchant burghs in much of the south and east, the Gàidhealtachd has been reduced massively to the present region of the Western Isles, and the North-West Highlands, Skye and Lochalsh and Argyll and Bute, with small Gaelic populations existing in Glasgow and Edinburgh.
The Highland Clearances of the 18th and 19th centuries also contributed to the decline of the language, as they reduced the population of the Scottish Highlands, which were predominantly Gaelic-speaking at the time.
Canadian Gàidhealtachd 
Scottish Gaelic has also survived among communities descended from immigrants in parts of Nova Scotia (especially Cape Breton Island), Glengarry County in present day Ontario, Prince Edward Island and Newfoundland (although Newfoundland had an Irish Gaelic-speaking population) in eastern Canada and those areas where Gaelic is spoken can also be said to be Gàidhealtachdan.
See also