A knot is used to express the speed of a boat. A knot is a unit of speed equal to one nautical mile per hour. In other words, it is about 1.8 km/h. Slow, eh? If you look up the word, “knot” in the dictionary, you will find the other “knot” (e.g. of a cord, rope, or the like). In the past, the speed of a boat was measured by a knotted rope.