Cloning is a method of asexual reproduction in plants
A clone in cannabis cultivation is a plant which was reproduced with a clipping from a mature plant of the same variety. The alternative method is to breed a male plant with a female plant in order to produce seeds, which is the typical method of sexual reproduction in the plant kingdom.
This method of plant reproduction is useful to ensure genetic purity and sometimes necessary in the event of a sterile plant strain which is no longer capable of sexual reproduction. Here is a very mellow CNN news interview on cloning:
Cloning is very common in agriculture. It’s used to produce everything from bananas to grapevines. Several plants reproduce by cloning themselves as well, such as aspen trees.