CBD stands for Cannabidiol.
Among the 60+ cannabinoids contained in hemp, only two are major components of it. Delta-9 tetrahydrocannabinol, or THC, is the molecule responsible for the psychoactive effect of cannabis. Cannabidiol, or CBD, is the other major cannabinoid.
It has no psychotropic or euphoric effect on the organism. In EU, this molecule is legal, whatever its concentration. The THC and CBD concentration of cannabis depends on the plant variety.
Some varieties have a very high concentration of THC and little CBD, others have almost no THC and are very concentrated in CBD.
The World Health Organisation has recognised CBD as both safe, non-toxic and with very few side effects.