An absolute epidemic of is, is is sweeping the airwaves and our personal conversations. What this phenomenon is, is the use of is twice in a row when defining something. And this usage is incorrect. This problem arises because people are leaving out the word that in noun clauses after the verb is.
When the word that is left out, a pause is needed to indicate that what follows is a noun clause. A comma correctly indicates the pause:
But having left out the word that and paused, apparently people are still feeling the need for a word to smooth over the transition, and we then hear that second, redundant is:
Years of experience have taught me that railing at TV commentators for such solecisms, or even worse, calling friends and family out on their sloppy sentence structure, does nothing for either their grammar or my reputation for being a fun person. So what are wordsmiths to do? Just don't perpetuate the double-is usage in writing. Then maybe this epidemic will pass without causing any permanent harm to our language.