A concealed-duct mini-split — also called a slim-duct, ducted, or horizontal-ducted air handler — is an indoor unit hidden out of sight in an attic, dropped ceiling, soffit, or closet, connected to short duct runs that feed supply grilles in one or more rooms. From inside the room you see only the grilles, not an indoor head on the wall. It brings inverter-driven ductless efficiency to a layout that needs distributed airflow.
The key spec is external static pressure (ESP) — how hard the unit's fan can push against ductwork. Low-static models are designed for very short, simple runs serving a room or two; mid-static models tolerate more ductwork and can cover a whole floor or several rooms from a single zone. Because the duct runs are short and the unit is matched to them, a concealed-duct system avoids the long, leaky duct losses of a conventional central system while still hiding the equipment.
Homeowners pick concealed-duct units for two reasons: appearance and coverage. Where a visible wall head is unwelcome — a primary bedroom suite, a finished room with no good wall, a design-led remodel — a ducted air handler disappears into the structure. And where one open head can't reach every space (a bedroom plus its bathroom and closet, say), short ducts spread the conditioned air without adding more outdoor units. The trade-offs are needing a concealed cavity to house the unit and a Manual D duct design so the static pressure stays within the air handler's rating; pushed beyond it, the system loses airflow and efficiency.