爆炸是某一物质系统在发生迅速的物理变化或化学反应时，系统本身的能量借助于气体的急剧膨胀而转化为对周围介质做机械功，通常同时伴随有强烈放热、发光和声响的效应。

爆炸的定义主要是指在爆炸发生当时产生的稳定爆轰波，也就是有一定体积的气体在短时间内以恒定的速率辐射性高速胀大（压力变化），没有指明一定要有热量或光的产生，例如一种叫三过氧化三丙酮炸药TATP，其爆炸只有压力变化和气体生成，而不会有热量或光的产生。而爆炸音的产生，主要是源自于爆炸时所产生的气体膨胀速度高于音速所致。

由于急剧的化学反应在一定被限制的环境内导致气体剧烈膨胀，这能使密闭环境的外壁损坏甚至破裂、粉碎造成爆炸的效果。爆炸还会破坏附近之物体与生物个体。另外天体撞击或雷击时引发之物理变化（包括伴随着之物体碎裂飞散与闪光等）亦可称为爆炸。

An explosion is a rapid increase in volume and release of energy in an extreme manner, usually with the generation of high temperatures and the release of gases. Supersonic explosions created by high explosives are known as detonations and travel via supersonic shock waves. Subsonic explosions are created by low explosives through a slower burning process known as deflagration. When caused by a man-made device such as an exploding rocket or firework, the audible component of an explosion is referred to as its "report" (which can also be used as a verb, e.g., "the rocket reported loudly upon impact".)