What is "photoperiodism"

1920, from photoperiod (1920, from photo- + period) + -ism.

n. (context biology English) the growth, development and other responses of plants and animals according to the length of day and/or night

Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods.