What is the meaning of the title of the Star Trek Discovery episode "An Obol for Charon"?
Charon, in ancient Greek mythology was the ferryman that carried the souls of the dead across the Stygian river into the care of Hades, god of the underworld. He required payment for this service, as he would.
Traditionally, coins were placed in the mouth of the deceased, ready to pay for their passage. An obol is a type of currency used in that time, a coin.
The mention of Charon would then portend death in some form or other.
The sphere that Discovery encounters, at first seems to be attacking them with tremendous energies, overpowering the sensors and communication-channels - in fact turns out to be giving-up all its millennia of observations and collected data of many civilisations in an attempt to pass all this on before it dies (or ceases to function, it's not made quite clear if it's living in any way).
So that turns out to be the "death" of the sphere that's being referred to.