A battle is an instance of armed combat in which military opponents attempt to defeat each other. Battles are usually considered to be one instance of conflict, even though they may be protracted (long and drawn out) and take place over hours or days. Successive military battles are often part of a larger war.
When several battles with the same goal are fought over time, they are often termed a campaign, which indicates both their focus and the fact that the battles took place over a lengthy period.
Unlike wars and campaigns, which may have multiple goals and be fought on more than one front, the object of a battle is usually specific, finite and easily-defined. The object of a battle is specific: to take or defend a certain position, or to seek out and engage the enemy, are common examples.
Most battles are forgotten in the larger context of war. Where battles are remembered, it is usually because they have been pivotal in the conflict, such as turning the tide of the entire war (the Battle of Gettysburg), they have signalled a complete rout of the enemy (the Battle of Waterloo) or they have changed the course of history (the Battle of Hastings).
Battles may also be remembered for being excessively gory, for having an unforgettable moment, or for being disastrous in concept or execution (Dunkirk, Gallipoli, The Alamo). Even battles that end in crushing defeats can galvanise nations; these may enter the national folklore and/or be remembered in the country's oral tradition, art, or literature (the Charge of the Light Brigade, the ANZAC tradition, Remember the Alamo!).
Other uses of the term
By extension, any protracted contest, argument, dispute or fight that can be likened in intensity to a military battle can be referred to as a 'battle'. In this sense, the conflict can be friendly or unfriendliness, and can be verbal, physical or mental.