Origins
The word "pagan" is middle English, derived from late Latin paganus meaning "country dweller", "civilian". Also from pagus, meaning "country", "rural district". Pag is Indo-European in origin and means "to fasten".

"C. Mohrmann suggests that the general meaning was any 'outsider,' -- a neutral term -- and that the other meanings, 'civilian' and 'hick,' were merely specialized uses of the term."†

Definition of Paganism
Wiccans, witches, Christian Wiccans, Neo-pagans (modern pagans), and more all call themselves "pagan". Since the word has taken on so many meanings, "pagan" has come to mean any religion that is Earth centered. "These are often Neopagan religions based on the deities, symbols, practices, seasonal days of celebration and other surviving components of ancient religions, which had been long suppressed."‡

It has been argued that Wicca and Paganism are two separate religions'; they are, as Wicca is centered around a pre-set Goddess and God. Paganism refers to a general polytheism including but not limited to Egyptian, Celtic, Hindu, Buddhist, Australian Aboriginal, Native American, etc pantheons.

Please visit Forms of Wicca for a definitive list.

† and ‡ taken from ReligiousTolerance.Org