Stroma: The supportive framework of an organ (or gland or other structure), usually composed of connective tissue. The stroma is distinct from the parenchyma, which consists of the key functional elements of that organ. The stroma of the thyroid gland is the connective tissue that supports the lobules and follicles of the thyroid gland.
The Greek word "stroma" means "anything spread out for sitting or lying upon," essentially a mat. The stroma in anatomy is thus the supporting tissue.