What does the phrase "St. Elmo's Fire" mean?
St. Elmo's Fire is an unusual weather phenomena that occurs when a long object is passed through a strong electric charge and creates coronal discharge. This can happen to the masts of ships during storms, and less commonly along electricity poles or even pointed plants. The "fire" itself is plasma produced by the electric discharge, and it has a blue color thanks to the high levels of nitrogen and oxygen in our atmosphere.
The name for St. Elmo's Fire comes from the patron saint of sailors, St. Erasmus of Formia. Elmo is a nickname for Erasmus, and sailors are those most likely to observe this mysterious blue flame in person. This weather phenomena was taken by sailors as a sign of good luck and an earthly manifestation of their patron saint.
There is also a 1985 film titled St. Elmo's Fire. The film has little to do with the weather phenomena, but the characters do frequent a bar called "St. Elmo's." There is mention of the weather pattern when one character tries to comfort another, stating that St. Elmo's Fire was something that made sailors hopeful.