The ICFP contest is an annual programming contest organized by volunteers every summer since 1998. The contest is open for any team of contestants who can compete through the internet. The teams usually have exactly 72 hour to sovle the problem. The contest gets its name from the annual ACM SIGPLAN International Conference on Functional Programming, where the prizes for the contest are presented.
The homepage of the contest used to be http://www.icfpcontest.org/ , but as of this writing that does not redirect to the latest contest. You can find a list of contests up to 2012 here, the 2013 contest here, possibly a full list on the conference's website.
This category is for programming languages related to the contest, typically domain-specific languages defined in the task specification.