NARTHEX

In early Christian architecture the Narthex was a portion of the church at the west end, separated from the nave by a low wall or screen and reserved for the catechumens, energumens, and penitents who were not admitted amongst the congregation. The narthex was of two kinds, exterior and interior: the former consisted of an open atrium arcade continued across the front of the church; in the latter, the aisle and gallery were returned across the nave. The outer narthex was sometimes used as a hall of judgment and for other secular purposes, and, after the sixth century, as a place of burial, while the inner narthex sometimes called the matroneum, was used, probably for certain persons of rank or distinction, rather than as a women's gallery.

Picture taken from : http://blog.beliefnet.com/stuffchristianculturelikes/2010/04/149-calling-the-lobby-the-narthex.html

Acknowledgement: http://www.newadvent.org/cathen/10704b.htm