What is the meaning of emission?

noun

• The act of emitting; causing to flow forth.
  • synonyms: emanation
• A substance that is emitted or released.
  • synonyms: discharge
• The release of electrons from parent atoms.
• Any of several bodily processes by which substances go out of the body.
  • usage: "the discharge of pus"
  • synonyms: discharge, expelling
• The occurrence of a flow of water (as from a pipe. ).