Definition
In the context of biomedicine and health, informatics is the study and practice of using computers, information technology and data to improve health outcomes and care. It is related to data science, but the variance in the definition of these two fields do not establish a clear relationship, with some indicating that they are the same, overlapping, or that one is a subset of the other.
One example of biomedical informatics is clinical decision support systems, which involve using a data science approach to determine the recommended course of action, as well as determining how best to design a system to interface with clinicians.
Further Resources
The Journal of the American Medical Informatics Association defines informatics broadly, and a number informatics sub-specialties: https://amia.org/about-amia/why-informatics/informatics-research-and-practice