It means it has three tips. It is a symbol of Indo-European origin, representing the three dimensions. It symbolizes life, death and resurrection, rebirth or reincarnation. It was used by the Celts.
Also triquel or triquetra, it is an Indo-European symbol, widely used by the Celts, as a triangular knot, the knot of eternity that represents birth, death and reincarnation with many geometric versions.