The I-cord is a tube knitted in the round with two double-pointed needles.  Elizabeth Zimmermann named it the Idiot Cord in honor of her accidental discovery of the simple technique. The I-cord is a perfect example of her attitude toward knitting: let it be fun, free of needless complications, and full of discovery. In this picture from The Opinionated Knitter, a wonderful collection of her newsletters, Elizabeth wears an I-cord attached to her glasses.  Once you learn to make one, you'll be searching around for anything that might be improved with an I-cord.