Parasitic ice was a form of ice that expanded rapidly, covering and eventually crushing everything it touched; Zareh noted he had once seen it enter a person's throat. Its growth accelerated in the shade, or as a result of a spider lightning strike.
The surface of the Colony contained glaciers of parasitic ice. In 3189, the USS Discovery crash landed on one of these glaciers and was nearly enveloped by the ice before it was pulled free by a tractor beam from Michael Burnham's ship. (DIS: "Far From Home")