Does it exist online and where can one find it? (For example, these [two](http://arminstraub.com/math/what-is-column) [sources](http://www.math.cornell.edu/~whieldon/What_is....html) are not official; is the longer one complete?)



Complete (possibly official) list of "What is..." articles from the Notices of the AMS
It seems they made a list in the meantime:


<http://www.ams.org/publications/notices/whatis/noticesarchive>


