Dry ice is a solid form of carbon dioxide. Carbon dioxide is a chemical compound containing one carbon atom and two oxygen atoms. It is colorless and odorless.
Dry ice is made in a chamber. The maker lets carbon dioxide expand to atmospheric pressure from a nozzle. Some of that liquid carbon dioxide vaporizes to cool the rest of it, which forms into crystals. Those crystals are compacted into blocks, which are sometimes chipped and made into smaller crystals again.
Dry ice is largely opaque or colorless and also odorless. When dry ice "melts" it leaves no water like traditional ice, but vaporizes into the atmosphere. Because it is odorless, dry ice must be handled in well-ventilated areas because the vaporized carbon dioxide can build up in potentially lethal concentrations.