When we talk about photoperiod, we mean the daily hours of light and darkness that any given living organism receives, while photoperiodism refers to the physiological reaction provoked by the length of day or night, and the way it affects the behaviour and development of these plants and animals.
In botany, each subspecies has its own specific photoperiod, but plants can be classified into three groups: short-day plants, long-day plants and day-neutral plants. Cannabis is a short-day plant (with the exception of Cannabis Ruderalis autoflowering varieties), which means that it needs long nights with over 12 hours of uninterrupted darkness to trigger flowering.
In the plant world, both the light intensity as well as the daily hours of light/darkness determine the biological functions of organisms, such as seed germination, growth, flowering and maturing processes. In this way, the development of plants can be activated or suppressed depending on lighting conditions, meaning that, for example, most plant species are unable to flourish unless they receive a certain number of hours of darkness.