Shatter is a solvent-based cannabis extract. Being a type of BHO, it uses butane to separate trichomes from the cannabis buds and trimmings and hereby concentrates the cannabinoids and terpenes found in the plant.
Trichomes are small, glass-like crystals found on the cannabis plant. These trichomes contain the highest concentrations of THC and other cannabinoids and terpenes.
All cannabis concentrates (different types of BHO, hash and even kief) are essentially made by harvesting and concentrating trichomes.