Definitions for "Sealed Enclosure"
An enclosure can either be ported or sealed. Unlike ported enclosures, which have a port that allows air to move in and out of the cabinet, sealed enclosures use the trapped air inside the cabinet as an "air spring" for the woofer. Compared with ported enclosures, sealed boxes are usually smaller and play deeper bass but need more power.
A loudspeaker cabinet without any vent or portholes. For a given sized enclosure, they are either not as efficient or don't go a low in the bass as ported enclosures.
An air tight enclosure that completely isolates the back wave of the driver from the front. Very tight, defined sound (with Qtc = 0.707) with very good transient response and power handling.