Argyle is a specific design or pattern of different colored diamond shapes. If your grandmother visits Scotland, she might bring you back an argyle sweater. If you're preppy, you might just wear it.
It's not unusual for knitters to work an argyle pattern into a sweater or a scarf, and it's particularly common for Scottish knitters. Kilts frequently come in various argyle designs, and Scottish Highlanders have traditionally worn argyle socks since the 17th century. The word itself was inspired by the tartan belonging to the Campbell clan, from Argyll in the west of Scotland.