Bowline

Make a fixed loop at the end of a rope.

Can loosen when unloaded or repeatedly shaken.

Step-by-step

Start with the standing part
Leave enough working rope below to form the large loop.
Bring the end down
Extend the working end below the standing part.
Make the small loop
Turn the end to the right, around the small loop, and across the front of the standing part.
Form the large loop
Bring the end down the left side, across the bottom, and back up on the right.
Come up through the opening
Pass behind the lower rim and through the small loop. Bring the end forward above its upper rim.
Go around the standing part
Take the end around the standing part from the right, behind it, and back on the left.
Return through the same loop
Bring the end forward across the upper side and down through the small opening, behind its lower rim.
Leave the tail inside
Bring out the short tail inside the large loop, beside its returning leg.
Check the bowline
The collar surrounds the standing part. Both passes share the small loop, and the tail stays inside the large loop.