WHATIS stands for 'World-wide Host-based
Acronym Translation Information System.'
It used to be a database on the PROFS (OfficeVision/VM) system that all IBMers used before somebody forced
them all to use Lotus Notes.
WHATIS is now Web-based rather than
Host-based, but the acronym has not
changed, unless you want to call it 'Web-hosted Acronym Translation Information System.'