Exactly. Plaid and checked have distinct meanings in AmE, and Myridon has described those meanings pretty well.Checked (also check, checkered) is not plaid in US English. A check is a pattern of squares in two colors. Plaid is can be more than two colors and the stripes can be uneven sizes.
That is very interesting, OEDAnd just to confuse matters further, "plaid" seems to have entered the French language quite recently as a word for "blanket" or "throw" (soft furnishings). "Plaids" may be plain, checked or with any other pattern.
plaid: Etymology: Origin uncertain; perhaps < the past participle of ply v.1 (compare forms at that entry), with original sense ‘a folded blanket or cloth’. Compare Scottish Gaelic plaide blanket, plaid (not tartan), coarse flannel (1659 or earlier), probably < Scots (see note below). Compare also Irish pluid blanket, perhaps a recent borrowing < Scottish Gaelic.
Tartan is a pattern consisting of criss-crossed horizontal and vertical bands in multiple colours. Tartans originated in woven wool, but now they are made in many other materials. Tartan is particularly associated with Scotland. Scottish kilts almost always have tartan patterns. Tartan is often called plaid in North America, but in Scotland, a plaid is a tartan cloth slung over the shoulder as a kilt accessory, or a plain ordinary blanket such as one would have on a bed.