Health Informatics is "the interdisciplinary study of the design, development, adoption and application of IT-based innovations in healthcare services delivery, management and planning." - Dr. R. Procter, Editor, Health Informatics Journal. From http://www.nlm.nih.gov/hsrinfo/informatics.html
What does that mean?
Practically, this means that, among others, health informatics deals with the following major areas: