WordNet (r) 3.0 (2006):

NIH
    n 1: an agency in the Department of Health and Human Services
         whose mission is to employ science in the pursuit of
         knowledge to improve human health; is the principal
         biomedical research agency of the federal government [syn:
         National Institutes of Health, NIH]

The Free On-line Dictionary of Computing (30 December 2018):

NIH

   The United States National Institutes of Health.