Positions on earth are defined by their longitude (how far east or west you are) and latitude (how far north or south you are). Both latitude and longitude are angles. A nautical mile is one minute of degree of longitude along the equator. (A nautical mile is a little more than a regular mile.) Traveling at $x$ knots means traveling at $x$ nautical miles per hour. Suppose you fly in a Lockheed SR-71 (the fastest jet ever built) along the equator at a speed of 1,800 knots (roughly the top speed of the SR-71). Ignoring issues of refueling and such, it takes you hours to fly once around the world. You leave after breakfast and are back in time for a late dinner. Some airplane!
Hint: Flying once around the equator you cover 360 degrees of longitude.