The term 'wool knot' refers to a type of yarn made from wool fibers. The two crossword solutions, BURL and NOIL, are both types of wool knots. BURL is a type of wool knot that is created by twisting the fibers together in a spiral pattern. NOIL is a type of wool knot that is created by combing the fibers together in a straight line. Both types of wool knots are used in knitting and weaving projects.