Birdcage

kwint's picture

Birdcage is a Cant term meaning cell, prison, or something similar. Sometimes Sigil is called a birdcage, though most Bashers just call it the Cage. Sometimes Carceri is called a birdcage, too.

Sources: 
The Planewalker's Handbook
Planescape, Dungeons & Dragons, their logos, Wizards of the Coast, and the Wizards of the Coast logo are ©2008, Wizards of the Coast, a subsidiary of Hasbro Inc. and used with permission.