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A hormone is a substance produced by [[glands|glands]],[[Cell|cells]] or [[organ|organs]] which transports a signal from one [[Cell|cell]] to another. They induce chemical changes at a cellular level and are necessary for development and growth along with many other features.&nbsp;Only small volumes of hormone are required to initiate a change in the cell's behaviour. Hormones are produced by all multicellular organisms, but are widely called [[phytohormones|phytohormones ]]in plants. Examples of such [[phytohormones|phytohormones]] are [[auxin|auxins]] and [[ethylene|ethylene]]

The word hormone derives from a Greek work meaning "to spur on".

Hormones can be categorised in many different ways, for example the way they reach the target cells ([[endocrine|endocrine]] vs&nbsp;[[exocrine|exocrine]]&nbsp;hormones), or the ways they interact with the target cell to induce a change ([[steroid hormones|steroid]] vs [[peptide hormones|peptide]] hormones).