Plants produce certain chemicals which regulate its various activity like growth, ripening, fruit development. We refer them as plant hormones. We also call them phytohormones and growth regulator as they control the growth of the plant.
Typical examples of plant hormones are:
Auxin: Promotes lateral branches in plants like the rose.
Gibberellin: cause shoot development.
Cytokinin: Promote cell division.
Abscisic Acid: Cause degeneration of old leaves.
Ethylene: causes ripening of fruits.