Pagan - comes from the Latin paganus, which appears to have originally meant "country dweller," or "villager." The members of the Roman army seem to have used it to mean "civilian." When Christianity took over the Empire and continued it under new management, the word took on the idea of "one who is not a soldier of Christ." Today, the word means "atheist" or "devil worshipper" to many devout monotheists. But those who call themselves Pagan use it differently; as a general term for native, natural and polytheistic religions, and their members.
Paleopaganism - refers to the original tribal faiths of Europe, Africa, Asia, the Americas, Oceania and Australia, where and when they were (or are) still practiced as intact belief systems. Of the so-called "Great Religions of the World," Hinduism, Taoism and Shinto fall under this category. "Mesopaganism" is the word used for those religions founded as attempts to recreate, revive or continue what their founders thought of as the (usually European) Paleopagan ways of their ancestors (or predecessors), but which were heavily influenced (accidentally, deliberately or involuntarily) by the monotheistic and/or dualistic worldviews of Judiasm, Christianity and/or Islam. Examples of Mesopagan belief systems would include the Masonic Druids, Rosicrucianism, Spiritualism, Crowleyianity, and the many African-American faiths (Voudoun, Macumba, etc.).
Neopaganism - refers to those religions created since 1940 or so that have attempted to blend what their founders perceived as the best aspects of different types of Paleopaganism with modern "Aquarian Age" ideals, while eliminating as much as possible of the traditional western dualism. Examples of these would be Gardnerism, Feminist Wicca, Alexandrian Wicca, and Saxon Wicca.