It can be a biography, but much more. It can include why and/or how the artists did his works, the historical precedence and/or historical impact of hods work, or the underlying concepts that drive the image.
"A monograph is a work of writing upon a single subject, usually by a single author. It is often a scholarly essay or learned treatise, and may be released in the manner of a book or journal article. It is by definition a single document that forms a complete text in itself."
http://en.wikipedia.org/wiki/Monograph
"The monograph has become synonymous with the study of an artist's life and his or her oeuvre. Significantly, for much of the twentieth century a monographic study was considered an appropriate model for the dissertation. With the greater focus on historical approaches to art and the advent of critical methodologies adapted from other disciplines, the monograph came to be associated most closely with museum-based scholarship."
http://muse.jhu.edu/login?uri=/journals/renaissance_quarterly/v060/60.3och.html
"The monograph has been notable for its fluidity and variety; it can be scrupulous and exact, probing and revelatory, poetic and imaginative, or any combination of these. In the nineteenth century, the monograph combined art-historical, biographical, and critical methods, and even added elements of fiction."
http://mitpress.mit.edu/catalog/item/default.asp?ttype=2&tid=10786
NOTE: (We could use Yahoo Answers Arts Top Contributor "LILI "on this on. She has a PhD in art history and a background in writing and analyzing scholarly works. I tried to email her with this query, but she doesn't have that option open. http://answers.yahoo.com/activity?show=ZphNGky5aa
