Academic and religious term for belief in or worship of multiple gods. Often contrasted with 一神論 (monotheism).
Polytheism was widely practiced in ancient Greece.
I wrote a report on the difference between polytheism and monotheism.
汎神論 is 'pantheism', identifying God with the universe, distinct from the multiple distinct gods of 多神論.
From 多 (many) + 神 (god) + 論 (theory/discourse). A Sino-Japanese compound formed in the modern era to translate Western concepts of polytheism.