Difference between nautical mile and regular mile?

Something I've always wanted to know but never bothered to look up....

http://www.howstuffworks.com/question79.htm :

A nautical mile is based on the circumference of the planet Earth. If you were to cut the Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is 1 nautical mile. This unit of measurement is used by all nations for air and sea travel.

A knot is a unit of measure for speed. If you are traveling at a speed of 1 nautical mile per hour, you are said to be traveling at a speed of 1 knot.
A kilometer is also defined using the planet Earth as a standard of distance. If you were to take the Earth and cut it in half along a line passing from the North Pole through Paris, and then measure the distance of the curve running from the North Pole to the equator on that circle, and then divide that distance by 10,000, you would have the traditional unit for the kilometer as defined in 1791 by the French Academy of Sciences.
A nautical mile is 1,852 meters, or 1.852 kilometers. In the English measurement system, a nautical mile is 1.1508 miles, or 6,076 feet.
To travel around the Earth at the equator, you would have to travel (360 * 60) 21,600 nautical miles, 24,857 miles or 40,003 kilometers

Weird Dream

In my dream, I was standing near the shoreline.  My friend, Liza, runs up behind me and says "Look at Chicago!".  I scan the horizon, and on what looks like a long pier, is supposedly Chicago.  Above it, there is this funnel cloud, that keeps touching down and going back and forth over the city.

Unsure of what it is, me and my friend run into a hotel, which is a few hundred feet away.  I get into the elevator, but Liza does not make it in.  I tried to open the door, but was too late.  I go up to the 25th floor.

I enter the room.  It looks like a bunch of gym showers.  There were at least three of them.  I hear knocking.  I apparently came in through the backdoor.  I go to the front door, but find a refrigerator blocking the hallway to the front door.  So, I have to move it before I get to it.  Liza is at the front door.  She says that she is the same way, in that she enters her house through the back door and ends up blocking the front door with things.

All of a sudden, I am on the roof.  It is very windy and rainy.
I see a blue and red helicopter fly over head, then lose control and slam into the roof of the adjacent building.  But the helicopter didn't smash into pieces.  It bounced up.  The helicopter is hanging off the edge of the building, where I am with someone on the roof who says that the pilot is passed out.

We scream and bang on the helicopter and the pilot finally wakes up.

He instructs me to start pumping this contraption a certain way.  When I start pumping it, the helicopter inflates like a toy and is eventually repaired.