Hormone is a chemical substance that is produced in one part of the body (by an endocrine gland) and is carried in the blood to other distant organs or tissues where it acts to modify their structure or function. Some cells release hormones that induce a response in the neighboring cells (paracrine function), or sometimes the hormones can act on the cells they are released from (autocrine function).
For a cell to respond to a particular hormone it needs to have specific receptors for that hormone, and once the hormone binds to the receptor specific chemical pathways are activated that lead to a response.
Examples of hormones are corticosteroids (from the adrenal cortex), growth hormone (from the pituitary gland) and androgens (from the testes).