Wikipedia definition of a raid:

Raid, also known as depredation, is a military tactic or operational warfare mission which has a specific purpose and is not normally intended to capture and hold terrain, but instead finish with the raiding force quickly retreating to a previous defended position prior to the enemy forces being able to respond in a co-ordinated manner or formulate a counter-attack. Within the tactical mission, a raiding group may consist of personnel specially trained in this tactic (such as commandos or guerrilla fighters), regular soldiers, or any organized group of combatants.

The purposes of a raid may include:

to demoralize, confuse, or exhaust an enemy
to ransack or pillage a location
to obtain property or capture people
to destroy goods or other things with an economic value
to free POWs
to kill or capture specific people
to gather intelligence.
with references to historical raids (Vikings, Native Americans, Mongols - that stuff).