Here's a breakdown:

* Nautical mile: A unit of distance used in maritime and aviation, approximately 1.15 statute miles (or 1.852 kilometers).

* Knot: A unit of speed equal to one nautical mile per hour.

Why is it called "knots"?

Historically, sailors measured speed by throwing a piece of wood (a "knot") attached to a rope into the water. The rope was marked at regular intervals. By counting how many knots passed over the side of the ship in a specific time period, they could estimate the ship's speed.

Key Points:

* Knots are primarily used in marine navigation and aviation.

* 1 knot is equal to 1.15 statute miles per hour or 1.852 kilometers per hour.

* It's important to remember that "knots" refer to nautical miles per hour, not regular miles per hour.

So, when someone says a boat is traveling at 20 knots, it means it's moving at 20 nautical miles per hour.