An interior window or doorway trimmed with casing but without a sash or door.
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
cased opening, trimmed opening
An opening between rooms which is finished with door-jambs and trim but does not have a door hung in it.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.