Page 108 - Berndt Sundsten "My First Book of Knots: A Beginner's Picture Guide"

Tautline knot

Here is a knot that you just have to know. What’s so great about it is that it
locks itself when it is weighted, but is easy to move when the weight is
removed. It is also called the midshipman’s hitch and the rolling hitch.

The tautline knot holds against sliding along the object on which it sits. For

example, if the knot is tied around a mast or a pole, it can be weighted
without slipping.