Short answers, pulled from the story.
An electron is a subatomic particle whose electric charge is negative one elementary charge. It is an elementary particle that, along with up and down quarks, makes up the ordinary matter of the universe.
In 1897 the British physicist J. J. Thomson, working with John S. Townsend and H. A. Wilson, showed that cathode rays were genuine particles rather than waves or atoms. By 1899 he found their charge-to-mass ratio did not depend on the cathode material, and he measured the corpuscles as roughly 1,400 times less massive than hydrogen.
The word derives from the Greek ἤλεκτρον, ēlektron, meaning amber, by way of the Latin ēlectrum. George Johnstone Stoney first coined electrolion in 1881, then switched to electron, writing in 1894 of his wish to suggest the name electron for the fundamental unit of electricity.
The American physicists Robert Millikan and Harvey Fletcher measured the electron's charge in their oil-drop experiment of 1909, with results published in 1911. They used an electric field to hold a charged oil droplet against gravity, measuring charges from as few as 1 to 150 ions with an error margin under 0.3 percent.
An electron is extremely lightweight, with a mass roughly 1,836 times smaller than that of a proton. It has the lowest mass of any charged lepton or electrically charged particle of any type.
Within the Standard Model the electron is considered stable, because as the least massive particle carrying charge, its decay would violate charge conservation. The experimental lower bound on the electron's mean lifetime is 6.6 years at a 90 percent confidence level.
Electron beams are used for welding conductive materials in a vacuum without filler, for electron-beam lithography that etches semiconductors down to about 10 nanometers, and for radiation therapy that treats superficial tumors. Electron microscopes use focused beams to produce atomically resolved images, reaching sub-0.05 nm resolution.