Dry ice, sometimes referred to as "cardice" (chiefly by British chemists), is the solid form of carbon dioxide. It is used primarily as a cooling agent. Its advantages include lower temperature than that of water ice and not leaving any residue (other than incidental frost from moisture in the atmosphere). It is useful for preserving frozen foods where mechanical cooling is unavailable.
Dry ice sublimes at 78.5 °C (109.3 °F) at Earth atmospheric pressures. This extreme cold makes the solid dangerous to handle without protection due to burns caused by freezing (frostbite). While generally not very toxic, the out-gassing from it can cause hypercapnia (abnormally elevated carbon dioxide levels in the blood) due to buildup in confined locations.
Dry Ice pellets are a convenient alternative to a solid block. They are smaller and easier to use. Most commonly used for small packages, pharmaceuticals, and for exotic drinks and shows.