OCU stands for old CAD user, as in CAD - Computer Aided Design. The 'old' part is a result of having been involved in using this technology since 1977, when interactive engineering software was very new.
For details on what CAD is and how it's used, try this sight:
http://en.wikipedia.org/wiki/Computer-aided_design
And for details of the particular version of the software that I was involved with, try:
http://en.wikipedia.org/wiki/Siemens_NX
And if you wish to dive really deep into the history of NX, try this site (note that 'NX' was once known as 'Unigraphics'):
http://www.plmworld.org/p/cm/ld/fid=209
OCU