A battle is a specific instance of combat in warfare between two or more parties or army's wherein each group will seek to defeat the others in various forms of combat, whether on a planet or in space. Battles are most often fought during wars, or military campaigns within wars, and can usually be well defined in time, space and action. Wars and military campaigns are guided by strategy whereas battles are the stage on which tactics are employed. German strategist Carl von Clausewitz stated that "the employment of battles to gain the end of war" was the essence of strategy.
An assault is a special type of battle involving an attack by one party, usually with the element of surprise.
A military campaign is a term applied to large scale, long duration, significant military strategy plan incorporating a series of inter-related military operations or battles forming a distinct part of a larger conflict often called a war. Notable examples include the Jovian Moons Campaign preceding the Interplanetary War, as well as the five-year Harvest campaign.
An insurrection is a rebellion conducted by a group of combatants, usually against a superior force. The many conflicts that comprised the human civil war known simply as the Insurrection, including the various Mamore insurrections, are perhaps the most notorious example.
A massacre, in military terms, is a battle where one party is routed and suffers complete or near-complete losses compared to the other party. Notable examples include the Massacre at Eridanus Secundus and the Massacre of Troy.
An operation is a planned military offensive, generally against a specific enemy objective or group of objectives. Operations can be large scale battles or small, covert insertions. Operations receive unique code words to distinguish themselves from other actions without giving away sensitive information should discussion of them be intercepted by enemy forces.
A raid is a sudden attack behind an enemy's lines without the intention of holding ground. Examples include Blue Team's Operation: SMOKING ACES in 2531 as well as the several raids on the Truth and Reconciliation during the larger Battle of Installation 04.
A siege is a military blockade of an enemy fortress with the intent of conquering by attrition and/or assault. Sieges involve surrounding the target and blocking the reinforcement or escape of troops or provision of supplies. Siege of the Atlas Moons is one notable example, along with the final years of the Battle of Charum Hakkor during the human-Forerunner wars.
A skirmish is a brief battle between small groups, usually part of a longer or larger battle or war. Examples of note include the naval skirmishes at Capella and Theta Ursae Majoris during the Insurrection.