What does sublimation mean?
Sublimation is a direct transition from solid to gas without passing through a liquid phase. The reverse transition is deposition. Dry ice turning into gas at normal atmospheric pressure is a familiar example.
Its place on a phase diagram
Phase stability depends on temperature and pressure. Below the triple-point pressure, heating some solids leads directly to gas. Sublimation requires energy and can cool the surroundings. Molecules can leave solid surfaces even at low temperatures, which helps explain why frozen laundry can gradually dry in sufficiently dry conditions.
Freeze-drying and practical limits
Freeze-drying first freezes a product and then removes ice by sublimation at low pressure. It can be useful for heat-sensitive materials, but does not guarantee every component remains unchanged. The white fog around dry ice is condensed atmospheric water rather than colored carbon dioxide gas. Carbon dioxide can accumulate, so dry ice requires ventilation and must not be sealed in airtight containers.