In North America, and predominantly in the United States, the words plaid and tartan are usually misapplied.

A plaid is a garment, and originates in the Gaelic word for blanket. Historically, 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.”

There are, however, also Irish tartans and tartans designed and produced for military, corporate and national purposes.

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 representative of a Scottish clan, is called a plaid. But this is a North American term, not a historically correct term for a tartan.