St. Elmo’s Fire is a weather phenomenon involving a gap in electrical charge. It’s like lightning, but not quite. And while it has been mistaken for ball lightning, it’s not that, either. 

St. Elmo’s Fire is plasma, or ionized air that emits a glow. St. Elmo’s Fire is a corona discharge, and it occurs when there is a significant imbalance in electrical charge, causing molecules to tear apart, sometimes resulting in a slight hissing sound. (Source)