The NIH Director's Panel on Clinical Research developed the following description:

• Patient-oriented research. Research conducted with human subjects (or on material of human origin such as tissues, specimens and cognitive phenomena) for which an investigator (or colleague) directly interacts with human subjects. This area of research includes:  mechanisms of human disease; therapeutic interventions; clinical trials; development of new technologies
• Epidemiologic and behavioral studies
• Outcomes research and health services research.

Note that this definition excludes in vitro studies utilizing human tissues that do not deal directly with patients.

By contrast, "clinical trials" assess the safety & efficacy of new therapeutics, vaccines, devices, or other interventions.  Clinical trials are divided into the following categories:  Phase I (small numbers of healthy subjects to determine safety and appropriate dose); Phase II (larger numbers of subjects to gather preliminary evidence of the effectiveness and major side effects of the intervention; Phase III (the "gold standard" for determining the efficacy of an intervention, with collection of data on rarer side effects - for use in drug labeling if approved by the FDA); and Phase IV (post-marketing studies such as comparison with other drugs on the market, longer-term estimates of effectiveness, effectiveness in a real-world setting, or examination of very rare side effects).