When we talk of a humidor, it is usually meant to indicate a box or a room where the humidity is maintained at a constant level. The requirement of a humidor comes up in order to preserve items such as cigars, pipe tobacco, cigarettes and others. Usually, for cigars a box of wood or acrylic glass is made to maintain the humidity.
The humidor rooms are those where the humidity is maintained at constant levels. Even for preserving baseballs, large rooms are created to maintain humidity so that the wood of the baseballs are preserved. Hygrometers are used to measure the humidity levels in such places.