Anthropology is the study of humanity. It's almost exactly the same as sociology really - sociologists and anthropologists don't spend much time worrying whether or not they're 'doing' anthropology or sociology - but the main difference is the history of the disciplines - anthropology started out as the study of what were then known as 'primitive' people, sociology the study of 'civilisation' or (then) contemporary European society. The difference NOW is that anthropologists tend to take a more comparative perspective of their work, ie, they might look at the effects of tourism in Birmingham, UK and Birmingham, US, for a cross-cultural point of view.
But then there are different types of anthropology - material culture, for example, which is a type of anthropology/archaeology cross over - indeed, anthropology has a great deal in common with archaeology.
Quite simply, anthropology is the study of humanity. A broad task, but it comes from the GReek etymology -
Anthros - man (human)
ology - Science.
Despite the person below's rebuttal I stand by my charge that most top anthropoogists and sociologists, at least in the UK, don't spend that much time worrying about whether what they're doing is one or the other. Indeed some of the most wel known anthropologists of our day have been multidisciplinary (cf, eg. Foucault, Milton, Ingold) I will provide a list of resources and a quotation later today when I've finished my final essay.