It seems to me that some Americans will say plaid where we will use tartan.
Whilst tartan refers to woollen cloth woven in one of several patterns of coloured checks and intersecting lines; plaid can refer to the same thing but, usually in the UK, it refers to a specific long piece of tartan worn over the shoulder as part of Highland dress.
Am I right in my belief that plaid is more often used by Americans to refer generally to the cloth? Are the two words used interchangeably? It would naturally be nice to receive a Scottish opinion on this.