According to Wikipedia's page on Christmas Controversy: "Although a close variant of the term "War on Christmas" is believed to have first been coined by British American journalist Peter Brimelow in 1999,1213 the concept of a modern-day "War on Christmas" only became widely discussed in the United States and Canada during the first few years of the 2000s decade, often credited particularly to an exposure of the issue by American commentator Bill O'Reilly.The claim among Brimelow, O'Reilly, and later a variety of prominent media figures and others was that any specific mention of the term "Christmas" or its religious aspects was being increasingly censored, avoided, or discouraged by a number of advertisers, retailers, government (prominently schools), and other public and secular organizations."

Mostly, the term is used to reference the sometimes heated disagreement between those who view public Christmas observance as a right versus those who view Christmas as a state-imposed endorsement of religious worship.