The study of a society or culture by examining what it discards.

{Garb(age) + -logy.}

"Though garbology remains a relatively unplumbed subject, several colleges and universities offer courses that look at what people throw away and how it reflects who they are."
Tina Kelley, "Class at N.Y.U. Looks for Deeper Meaning at Fresh Kills," The New York Times, Mar 23, 2000.

Apparently this study was first named by Professor William Rathje of the University of Arizona; it is part of archeology studying the past, studies of current lifestyles, and recycling/landfill management.

Sources: http://itech.fgcu.edu/&/issues/vol2/issue2/garbology.htm, http://training.egyptian.net/~leftypen/garbology.htm