Foresic anthropology is the science of physical anthropology and osteology combined in a legal setting.
A forensic anthropologist usually works at a crime lab and examines the bones of the deceased if the body is either burnt, badly decomposed, mutilated or otherwise unrecognisable and a standard autopsy cannot be performed. They are specialists in osteology (the study of bones) and anthropology (the study of what it means to be human etc.) Usualy, a masters degree and a phD is required to become a forensic anthropologist. They can determine things like, age, gender, ethnicity and height.
So basically, a forensic anthroplogist examines skeletal remains to determine things about someone that cannot be discovered through autopsy. The TV show 'Bones' (FOX or Sky, for UK viewers) is about a forensic anthropologist.