Half-space landing
1. 
2. A stair landing at the junction of two flights which reverses direction, making a turn of 180 degrees. Such a landing includes the width of both flights, plus the well. See also: Landing
Illustrated Dictionary of Architecture Copyright © 2012, 2002, 1998 by The McGraw-Hill Companies, Inc. All rights reserved
halfpace, half-space landing
A stair landing at the junction of two flights which reverses the direction of horizontal progress, making a turn of 180°. Such a landing extends the width of both flights plus the well.
McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.