Endocrine system refers to the system of glands that release their secretions (hormones) directly into the circulatory system. It is system of glands that produce endocrine secretions that help to control bodily metabolic activity.
Other /More definition:
Endocrine system is defined as the bodily system of ductless glands that secrete hormones into the blood to stimulate target organs; interacts with nervous system functioning; system of glands that produces many different hormones