闪电，在大气科学中指大气中的强放电现象。在夏季的雷雨天气，雷电现象较为常见。它的发生与云层中气流的运动强度有关。有资料显示，冬季下雪时也可能发生雷电现象，即雷雪，但是发生机会相当微小。若有严重的火山爆发时，或是原子弹爆炸产生昙状云，空中可能因短路而发生闪电。

闪电的放电作用通常会产生电光。雷电起因一般被认为是云层内的各种微粒因为碰撞摩擦而积累电荷，当电荷的量达到一定的水平，等效于云层间或者云层与大地之间的电压达到或超过某个特定的值时，会因为局部电场强度达到或超过当时条件下空气的电击穿强度从而引起放电。空气中的电力经过放电作用急速地将空气加热、膨胀，因膨胀而被压缩成电浆，再而产生了闪电的特殊构件雷（冲击波的声音）。目前对于放电具体过程的认识还不能透彻明白，一般被认为和长间隙击穿的现象相类似。

Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud (called intra-cloud lightning or IC), between that cloud and another cloud (CC lightning), or between a cloud and the ground (CG lightning). The charged regions in the atmosphere temporarily equalize themselves through this discharge referred to as a strike if it hits an object on the ground, and a flash if it occurs within a cloud. Lightning causes light in the form of plasma, and sound in the form of thunder. Lightning may be seen and not heard when it occurs at a distance too great for the sound to carry as far as the light from the strike or flash.