The lip ruler is probably the Olipfa ruler, 5x18" or 5x24" long. It has a small ledge on one end, underneath the ruler so that as you line it up along a straight table edge or the edge of your cutting mat, it acts as a barrier to keep the ruler from sliding. Gives you straighter cuts because the ruler tends not to slip when you are cutting long (such as 18-22") cut strips. It works like a t-square would for engineers. Walmart, Joannes and other chain places carry them.
Jan in VA