Thermion is a term used to describe a stream of electrons emitted by a heated source. Some common synonyms for the term include thermoelectron emission, thermionic emission, and Edison effect, named after Thomas Edison who first discovered this phenomenon. Other related terms often used interchangeably with thermion include electron discharge, space charge, and vacuum emission. Understanding the language of thermionics can aid in the study of electronics, particularly vacuum tubes and electron microscopy. Regardless of the term used, thermion refers to the same physical phenomenon: a heated surface or filament emitting a cloud of electrons into a vacuum, leading to electric current and the ability to manipulate electrons for technological purposes.