Don't even think of referring to it as plaid — it's tartan. Tartan is a special pattern that originates from the Scottish highlands; every April 6 we celebrate National Tartan Day. Historically, different regions and later, clans, would have different and unique tartans, since each tartan was made by a local weaver. Today, there are thousands of different "official" tartans and many endless unofficial ones. See how tartan differs from other patterns and celebrate by wearing your own tartan-patterned clothing today.

Image from Flickr user Michael Coghlan.