the.com/running knot

means A loop knot, like a slipknot or noose, that slides along its own standing rope to cinch tighter under tension.

from Straightforward compound of 'running' (moving, sliding freely — as a rope 'runs' through a pulley or loop) and 'knot.' The phrase dates back centuries in English rope-work and sailing vocabulary, describing any knot built so the loop isn't fixed but slides along the line, letting it constrict as one end is pulled — the same mechanical idea behind a slipknot, a noose, or a drawstring's working end.