Taken from the article What is an Electron? by Peter Ripota

• Electrons exist in two forms: free and bound.
• Free electrons are found in metals & the air, while bound electrons exist in atoms.
• Charge and mass are the same for all electrons.
• Electrons spin up or down (counterclockwise or clockwise)
• The diameter of its orbit around the atomic nucleus, is known as the energy level.
• Electrons are the only elementary particles that live forever (that are stable).
• Electrons are the only particles observed traveling faster than the speed of light.
• Electrons were the first particles to reveal their wave nature, even though they are clearly particles. 
• In string theory, they are incredibly small vibrating strings that can be stretched incredibly far.