The first definition of Paganism that I offered, that of Prof. Michael York, should be placed in its context, which was primarily the academic study of religion. (Amazon link to York’s published books.)
When it was published in 2003, academic interest in the study of contemporary (or neo-) Paganism had been growing, but primarily from the point of view of Paganism as a new religious movement.
Within the academy — and here I speak mainly of the American Academy of Religion, the largest body for such study on this continent (it includes many Canadians too) — even the study of new religious movements was way off to the side. Those scholars themselves were relative newcomers to the AAR, which had its origins in the study of Christianity and which devoted most of its program sessions to textual matters.
York not only situated Paganism as “a religion, a behavior, and a theology,” he argued that Pagan elements were found in other “world religions” too — not just “Pagan survivals” but behaviors, primarily.
I don’t mean to suggest cause and effect — one book did not do that — but it was at about the same time that the AAR’s leadership, which had rejected a proposed Pagan Studies program unit — a permanent slot, in other words — in 1997, relented in 2004 and granted it.
So York helped to forge a sort of non-sectarian (not Wiccan, not Asatru, not Roman reconstructionist, etc.) definition that would change people’s minds to where they no longer thought that the P-word meant “having no religion” or “follower of an obsolete religion from long ago.”
Instead, it would be a type of religion or a way of being religious. Paganism (academic definition) was everywhere.