A full explanation, diagrams, and examples, can be found on Les Cowley's brilliant Atmospheric Optics site, here.
There was an amazing sunset here in Christchurch on January 17th. Clouds near the setting sun cast shadows across the sky that resulted in dramatic contrast between sunlit and shadowed air.
This was the view towards the sun:
This was the view to the north. You can see the rays' paths across the sky, travelling to the east...
At the anti-solar point in the east, the rays appear to converge. Around the anti-solar point these are known as 'anti-crepuscular' rays:
Crepuscular rays and anti-crepuscular rays are different ends of the same phenomenon, as can be seen in this wide-angle image taken of the same January 17 sunset at Birdlings Flat, some 50km from where I took my photographs.