All matter is made up of atoms. An atom has protons, which are positively charged, in its nucleus, and the same amount of electrons orbiting about the nucleus. As electrons are negatively charged, an atom is in equilibrium, or balanced, when it has not lost an orbiting electron. When an atom has lost an electron, it becomes a positive +ion, since it contains more protons than the negatively charged electrons. When it has gained one, we call it a negative -ion, since it now has more negatively charged electrons than positively charged protons. So, when one atom loses an electron, it will always tend to draw, or gain, a new one towards itself to recover its internal equilibrium.
Not all materials allow this constant flow of electrons when the conditions for which are created. There are good materials and bad ones. The materials which allow the flow of electrons are called conductive materials. Those that do not allow are called non-conductive materials. For example, metals are excellent conductors, specially aluminum and copper. On the other hand, materials such as wood, glass, and plastic are non-conductive materials, or insulating materials.
In electricity this flow of electrons within a conductor is called electric current. And there are two kinds of electric current. Direct current and alternating current.