its a mathematical knot, which is essentially definable as a loop of &quot;string&quot; that has crossings that cannot be removed (ie the loop returned to a normal doughnut shape&#x2F;torus) via any sort of transformation that doesn&#x27;t involve cutting it.<p>the trefoil in the article is an example of such a thing.<p>Most knots we encounter in every day life are not a knot in a mathematical sense, because they can be untied, or don&#x27;t form a loop.