According to Wikipedia, a bowline knot is "an ancient and simple knot used to form a fixed loop at the end of a rope. It has the virtues of being both easy to tie and untie; most notably, it is easy to untie after being subjected to a load. The bowline is sometimes referred as King of the knots because of its importance. It is one of the four basic maritime knots (the other three are figure-eight knot, reef knot and clove hitch)."
Want to try making a bowline knot? Form a small loop leaving enough rope for the desired loop size. Pass the end of the rope through the loop as though making an overhand knot. Continue around the standing end and then back through the small loop.