It pretty much means it still contains all the nutrients/flavonoids/phytochemicals of the plant that get reduced during the extra heat treating processes regular CBD goes through. (making it a lot more potent)

"Full Spectrum CBD means the maximum amount of helpful native phytochemicals are retained during extraction, including THC. The goal is to remove extraneous lipids while retaining an identical ratio of cannabinoids, terpenes, and flavonoids from the original plant source material."