Definitions for "encased"
covered or protected with or as if with a case; as, products encased in leatherette.
This means that the organ (or a division, if it is used to describe only one division) has its pipes inside one or more wooden cabinets or Cases, which consist of sides, back and top. Their resonance serves to refine and blend the sound and project it into the room, providing an ideal environment for development of the tone. Such cases, sometimes called reflective cases, can be very decorative, and often have a facade of large pipes across the front.
A stamp inserted into a small coin-size case with a transparent front or back. Such stamps were circulated as legal coins during periods when coins were scarce.