Official Aviation Definition
A knot (kt) is a standard unit of speed defined as one nautical mile per hour. Since one nautical mile represents one minute of latitude on Earth, navigation and wind calculations are simplified by using knots universally across commercial and military aviation.
In Simple Words
The universal speed unit in aviation. 1 knot means traveling one nautical mile in one hour.
Real-World Flight Example
The air traffic controller asked the pilot to maintain 210 knots indicated airspeed until passing the outer marker.