Forms-of-Life

I have a vague understanding of what the concept of a form-of-life is, but, ultimately suspect that Giorgio Agamben had failed to adequately describe his philosophical concept in The Use of Bodies. Tiqqun describes them in Introduction to Civil War, and, while I do like the text, I honestly don't really know what a "form-of-life" is. I know that Aristotle had a similar concept and am unsure as to how much of his theory Agamben incorporates. I also know that Paolo Virno discusses forms-of-life in Essays on Negation. He seems to incorporate both Agamben and Wittgenstein's theories of the concept. How do Agamben, Aristotle, and, Wittgenstein's concepts of "forms-of-life" differ and what exactly is Giorgio Agamben's concept of a "form-of-life"?