The NIH recently updated their definition of what a clinical trial is. Here is the link to the new definition. Also worth reviewing are an FAQ list, some case studies, some additional training resources, and blog posts on September 8, 2017 and September 11, 2017.
National Institutes of Health. Notice of Revised NIH Definition of “Clinical Trial”. Notice Number: NOT-OD-15-015. Available at https://grants.nih.gov/grants/guide/notice-files/NOT-OD-15-015.html.