A Freezer is a type of storage device to preserve substances using low temperatures.
Most vary in size ranging from medium sized boxes to containers large enough to hold a single Terran. Though not as complex or effective as a stasis tube in keeping organic materials cold, they can be altered with more advance technologies to handle certain tasks.
Some can store nuclear devices or Zerg samples for military purposes. In recent times, they are used to prevent or measure the rate which zerg tissue mutates. Through this research, many scientists find out how the alien cells react to different stimulation. There are concerns of the samples adapting to the cold, so many research facilities keep them stored in areas that can be quarantined and sterilized in an instant (i.e. flamethrower traps, radiation projectors, and moderately to heavily armed Marines).