Vacuum drying is a process in which materials are dried in a reduced pressure environment, which lowers the heat needed for rapid drying. It does not take place in a true vacuum, despite the name. Devices used for vacuum freeze dryer are known as vacuum driers, and can vary in size from small units designed to fit on kitchen counters to massive rooms which are used to handle things like timber products.

Drying involves reducing the moisture in an object, and is done in environments where the air is drier than the object being dried, which encourages moisture to evaporate out. This is often accomplished with heat to reduce the humidity of the air, but in a vacuum drying equipment, the temperature does not need to be as high, and the drying is often faster. It's also possible to achieve a very high level of dryness, which may be desirable in some cases.