When is a tartan, a plaid? A plaid, a tartan?

The Tartan Weaver's Guide

Prior to receiving this question I had maintained that a tartan was a design registered with the Court of Lord Lyons in Britain, representative of a Scottish clan, a military regiment, a corporation, even a fashion design (such as Burberry). To me, everything else was just plaid.

It turns out I wasn't wrong, but it wasn't the whole story either.

Historically, a plaid is a garment, and originates in the Gaelic word for blanket. Ancient Scots wore belted and unbelted plaids, or large blankets gathered around the waist or as large shawls. As modern Highland dress, plaid refers to any tailored or untailored garment about the shoulders. Regardless of the pattern or colour, plaid traditionally refers to clothing.

Plaids, the garments, were often of a pattern, including tartan patterns. Tartans are representations of clan membership. The combination of colours, the pattern in which they are woven and thus intersect, and the resulting pattern of colour tones and half-tones make up a tartan. Typically tartans are symmetrical, the pattern repeating in setts or at regular intervals, although some tartans, and in particular old unnamed tartans, can be asymmetrical.

Thefreedictionary.com describes a tartan as "any of numerous textile patterns consisting of stripes of varying widths and colors crossed at right angles against a solid background, each forming a distinctive design worn by the members of a Scottish clan."

While accurate, this definition isn't complete. There are also Irish tartans and tartans designed and produced for military, corporate and national purposes. Irish clans did not typically have clan tartans, unless they emigrated to Scotland and either established a clan there or came under the protection of a Scottish clan.

The Irish tartans available commercially were commissioned by a U.K. weaving company, are named after the Irish counties and not registered with any tartan authority.

In North America, any textile in a pattern of criss-crossing lines of varying colour and width, that is not a tartan, and thus not registered as representative of membership in a Scottish clan, is called a plaid. But this is a North American term, not a historically correct term for either a plaid or a tartan.