1. \E*lec"tron\, n. [NL., fr. Gr. 'h`lektron. See
   {Electric}.]
   Amber; also, the alloy of gold and silver, called {electrum}.
   

2. \E*lec"tron\, [NL., fr. Gr. ?. See {Electric}.]
   (Physics & Chem.)
   One of those particles, having about one thousandth the mass
   of a hydrogen atom, which are projected from the cathode of a
   vacuum tube as the cathode rays and from radioactive
   substances as the beta rays; -- called also corpuscle. The
   electron carries (or is) a natural unit of negative
   electricity, equal to 3.4 x 10^{-10} electrostatic units. It
   has been detected only when in rapid motion; its mass, which
   is electromagnetic, is practically constant at the lesser
   speeds, but increases as the velocity approaches that of
   light. Electrons are all of one kind, so far as known, and
   probably are the ultimate constituents of all atoms. An atom
   from which an electron has been detached has a positive
   charge and is called a coelectron.
   

A sub-atomic particle with a negative quantised charge. A flow of electrical current consists of the unidirectional (on average) movement of many electrons. The more mobile electrons are in a given material, the greater it electrical conductance (or equivalently, the lower its resistance).