My husband's clan motto means something like "Never admit you are wrong" (in poetic wording of course. But apt, based on all the members I have met.) "Our" tartan is the Gordon, which is like the Black Watch but with a thin yellow stripe added. The really funny thing is, when I worked in South African townships (which also understand "clan"), that tartan was super popular because of the political significance of black, green and gold...
No personal Scottish ancestry here. But based on having 3 daughters who were Highland dancers: The pattern of the fabric is called tartan. Some tartans actually can have only two colours, but the width of the stripes varies, so you would never mistake it for gingham (which is symmetrical). A plaidie (pronounced by us Canadians as "pladdy" but who knows how they say it in Scotland) is a swath of tartan fabric worn pinned over one shoulder and draped down the back (with a fold in it suitable for carrying your lunch when you go to the fields). It is part of the aboyne (SP?) which is the formal costume worn to do the "girlie" dances. (For the "guy's" dances they wear the kilt, although only chromosomal boys are allowed to wear the sporran--as my daughter told me when I admired Rabbit's outfit to her and now I see that purse everywhere...)
And for those who are getting into Outlander: the piece of tartan fabric, worn historically by the men wrapped as a kilt or used as a blanket, cloak, or whatever is desired: that is called a plaid, and that I think is pronounced "played". (The ancestor of the plaidie as well as of the kilt.)
And as for the Black Watch: when I wore it, as a plaidie with a long dress to a formal Robbie Burns Dinner, I was told off that now "anyone" is allowed to wear that tartan, you have to be a member of the military regiment to be allowed to wear the cockade on your bonnet (sprig of tartan with a feather on your cap). Since I have never been tempted to, that won't be a problem.
Sorry for all the rambling, time for bed!