Sorry, can’t resist!
In Scotland, it’s called tartan and there are specific tartans for each clan. So, for example, as a Grant, I’d only ever wear the Grant tartan.
A ‘plaid’ is the long piece of tartan fabric that you will see over the shoulder of a man wearing the kilt (usually attached with a broach of the clan coat of arms).
The plaid comes from the original pre-18th century kilt that was adopted after King George III (of the American Wars of Independence fame) came to Scotland on a rare visit and wore his interpretation of the kilt (complete with pink tights). The kilt most folk are familiar with is this version, 8m of sewn pleated fabric belted at the waist.
The original kilt, which is still worn, was a 6-8 metres length of woollen tartan fabric. It is pleated & laid on top of your belt on the floor. The man lies on top, wraps the pleated fabric around his waist, securing with the belt.
The remaining long length under the top of his body is brought round and draped over the shoulder or just left to hang down behind. This is the ‘plaid’. Useful for protection from the weather, carrying things & for sleeping under at night.
Generally, however, we don’t wear tartan that often! Kilts or tartan troos (trousers for lowlanders usually for formal dress), woollen tartan travel rugs, maybe some accessories. Nobody would ever consider an outfit such as the one modelled above!!! Even in the period when it was fashionable elsewhere.
Anyway, a brief history of ‘plaid’ for you! ?