Wizard's Knot
The most basic energy-locking symbol of the Speech, used to end or begin many wizardries in their written forms. The Knot is a three-dimensional symbol with several widely accepted two-dimensional rationalizations used when diagramming a spell "in the flat". (The rationalization most commonly used by wizards on Earth is the so-called 74 knot -- a seven-crossing knot with four major lobes. A simpler "infinity-symbol"-like figure-eight variant is also popular.)
Topologically, the Wizard's Knot is described as "non-trivial" -- and wizards would agree with this for reasons that have nothing to do with topology. The Knot (like all other knots) is an expression of a closed circle, or (in higher-order versions) a sphere, embedded in three-dimensional space. This makes it the perfect symbol both of the spell as a complete and working structure without beginning or end, and of the continual intervention of the Powers That Be (through wizards) in the universe they assisted in creating under the auspices of the One.
The Knot is often used in spells for philosophical, structural or aesthetic purposes, rather than because it's strictly necessary in a wizardry. However, there are some spells which cannot be correctly completed without the Knot, or in which the wizardry is itself merely a large incidence of the Knot with other symbols added: examples would be the various wizardries used to invoke a temporospatial claudication, and also many stasis spells. (SYWTBAW et seq.)
See also: Euphemera: N-spheres: Spells (general composition and design): Sphere slicing: Topology (wizardly applications).