A conflict involving the organized use of arms and physical force between countries or other large-scale armed groups. The warring parties hold territory, which they can win or lose; and each has a leading person or organization which can surrender, or collapse, thus ending the war.
By extension, any conflict, or anything resembling a conflict.
(rhetorical) A campaign against something, the war on drugs is a campaign against the use of narcotic drugs; the war on terror is a campaign against terrorist crime.
(by analogy, business, countable) A bout of fierce competition in trade.
I reaped the benefit of the car dealerships' price war, getting my car for far less than it's worth.
The cellular phone companies were engaged in a freebie war, each offering various services thrown in when one purchased a plan.
(by analogy, uncountable) A particular card game for two players.