In biology, a strain is a genetic variant of a microorganism, plant, or animal. Cannabis plant strains are variations of the same species from the same ancestor.
Cannabis is believed to have evolved in Central Asia, reached other regions, and adapted to different climates over time. These changes resulted in new strains, landrace strains, that were better suited to their environments. Landrace strains are often named after their region of origin. They have different phenotypes native to their environment. Eventually, these landrace strains were crossbred to create the modern cannabis strains that exist today.
The main cannabis strains are indica and sativa, and hybrids are a mix of the two and other strains. One of the significant differences between strains is the flavor profiles, which are determined by the terpenes. Other differences are seen in the physical appearance and the effects, primarily determined by the cannabinoids.