There is no explicit licensing information at the TREC site, the statement below was
taken from the original OHSUMED corpus available here:

	http://ir.ohsu.edu/ohsumed/ohsumed.html 

The National Library of Medicine has agreed to make the MEDLINE references in the
test database available for experimentation, restricted to the following conditions:
1.  The data will not be used in any non-experimental clinical, library, or other setting.
2.  Any human users of the data will explicitly be told that the data is incomplete and out-of-date.