Electrons are subatomic particles. They are negatively charged.

According to Niels Bohr's atomic model, electrons go around / orbit the nucleus of an atom at discrete energy levels or shells. The outer most shell of an atom is called the valence shell and the electrons in this shell are known as the valence electrons.
 
Atoms can form bonds by
 
o   donating or accepting electrons (forming ionic bonds).
o   sharing electrons (forming covalent bonds).
 
In metals, electrons form "clouds" which bond the atoms together. This is known as the metallic bond.
 
If a potential difference is created between two parts / terminals of a piece of metal, the electrons will flow. The flow of electrons (which are charges) is referred to as the electric current.

See also the other subatomic particles: protons and neutrons.

     
Elektron merupakan zarah subatomik. Elektron bercas negatif.

Menurut model atom Niels Bohr, elektron-elektron mengorbit nukleus atom pada aras tenaga atau petala-petala tertentu. Petala elektron yang terluar (terjauh daripada nukleus) dikenali sebagai petala valens. Elektron-elektron yang berada di petala ini dipanggil elektron valens.

Atom-atom boleh mengikat secara

o   menderma atau menerima elektron (membentuk ikatan ionik)
o   mengongsi elektron (membentuk ikatan kovalen).

Dalam logam, elektron-elektron membentuk "awan" yang mengikat atom-atom bersama. Ikatan begini dikenali sebagai ikatan logam. 

Sekiranya perbezaan keupayaan diwujudkan di antara dua bahagian / terminal sesuatu logam, elektron-eletron akan mengalir. Pengaliran elektron-elektron (yang merupakan cas) juga dipanggil aliran eletrik.

Baca juga zarah-zarah subatomik lain: proton dan neutron.