HPCC stands for High Performance Computing Cluster, an open source software project created by LexisNexis.
In LexisNexis' usage is data processing that cannot be accommodated by a single machine. The answer is to split up the data and the processing so you can have from several to hundreds (or perhaps thousands) of machines all working away at pieces of a larger problem.
There's a significant Clarion connection here: many of the developers who created Clarion for Windows now work for LexisNexis, and specifically they're on the team that created the High Performance Computing Cluster (HPCC) product. The HPCC team includes a number of former Clarion folk such as Bob Foreman, Richard Taylor, Jim DeFabia, Richard Chapman, David Bayliss, Gordon Smith and the late Nigel Hicks.
In October 2011 Bob Foreman gave a presentation on HPCC at the Clarion DevCon. Read the report in Clarion Magazine.
In Feb 2012 HPCC announced a one-click solution for deploying an HPCC cluster in the cloud.
Mike Hanson points out that HPCC is on Twitter @hpccsystems. Also, Bob Foreman mentioned that there is a Facebook page: HPCCSystems