Clinical trials are interventional studies and involve investigational medicinal products, whereas clinical studies can include both interventional and non-interventional studies but do not involve investigational medicinal products.
The regulations for registering and reporting a clinical trial are different from those of a clinical study.
Phoenix Fundamentals: Clinical trial vs clinical study – synonyms or significant differences
Official Journal of the European Union: Regulation on clinical trials on medicinal products for human use, 2014
Clinical trials registry in the European Union (EU) and the European Economic Area (EEA)
Database of privately and publicly funded clinical studies conducted around the world