A perfect shuffle is called a &quot;riffle&quot;. Sometimes &quot;perfect riffle&quot; or &quot;perfect shuffle&quot; or &quot;perfect riffle shuffle&quot;. :)<p>A perfect riffle performed several times in a row will return a deck to its original state, it cycles. Its obviously hard to perform, but apparently possible with practice.<p>I don&#x27;t know if imperfect riffling can decrease randomness, and I&#x27;m open-minded but skeptical. I think it just takes a long time to achieve uniform randomness if the shuffling is bad. Good shuffles can randomize a deck after just a few shuffles. Bad shuffles can take a very long time.