Gland

A gland is a group of cells in the body which make substances such as hormones. They are in humans and other animals, and in plants. 
If the substance is put directly into the bloodstream, the gland is called endocrine gland. 
If the substance is carried by a duct, the gland is called an exocrine gland. Exocrine  ducts empty outside the body, or into cavities inside the body.

Examples of glands in humans are:
Sweat glands that produce sweat for perspiration.
The pineal gland in the brain, which produces the hormone melatonin at night.