The current revision on Wikipedia, beautifully abstract, describes a knot as an "intentional complication in cordage." But whether artful or utilitarian, every knot is also a set of instructions crystallized. Knots can encode a tactile canvas of numbers, binaries, or narratives. They can turn lines of string into complex forms of information: "string stories" convey myths in many cultures, knotted quipu preserved numerical data for Inca civilization, and scouting movements use knots to remember all manner of survival skills.
The more abstractly you think about knots, the farther you can drift toward the mathematics of topology and the structure of the universe itself. Below are several channels on the topic, knitted together with overlapping links and loops of their own.