There are many different types of cannabis to choose from. They sometimes have amusing names, such as Amnesia Haze, Sour Diesel and Purple Kush. They are all different from each other, and there are various properties that make them different.
In popular culture and terms, the strains of cannabis are actually cultivars. Each individual strain has been bred to have certain characteristics by the cannabis breeder. Some other names are Granddaddy Purple, is one strain and Harlequin is another one, for example. The former strain, Granddaddy Purple is a strain that induces sleepiness, that contains high levels of THC, which produces a psychoactivelly euphoric feeling. The second one mentioned, Harlequin, is a flower that has both CBD and THC. The cannabis plants with various names have been bred differently, and possess different characteristics, so they are likewise different strains of cannabis.
The word which classes the various types, of strains, is not without some controversy. Scientifically speaking, the term strain makes little sense, but that is the name that is used in popular culture. The semantic difference is that in the field of botany, different plant varieties are actually cultivars, as mentioned above, but not strains. That term is generally used for viruses and bacteria, but not plants.
In the cannabis world, the word strain started to be used in the 1980s, and has not changed since. The term is still prevalent in popular culture, and most dispensaries and cannabis aficionados still use it to refer to different types of cannabis. Since there are new levels of cannabis legalization, there are also newer scientific and technical terms to describe the plants. These are becoming increasingly popular.