ENDLESS KNOT

 
The endless knot or eternal knot is a closed, graphic symbol composed of right-angled, intertwined lines. Overlapping without a beginning or an end, it symbolizes many things, particularly in Buddhism.  For example it can mean:

The Buddha's endless wisdom and compassion.

Samsara, the cycle of birth, death, and rebirth. 
 
The eternal continuum of mind.

Principally, however, it represents how all phenomena are joined together as a closed cycle of cause and effect.

Cause and effect in Buddhism is the basis of karma.  The law of karma states that every action has a consequence, and every consequence is itself an action with a consequence, and so on, without end.

Karma continues without end, except, that is, for those who, either by their own effort in this lifetime or by their spiritual evolution over many lifetimes, gain enlightenment.  Those who break the cycle of karma enter nirvana; those who don't continue in the cycle.