Static electricity is that annoying little electric shock you sometimes get when touching a door handle, closing the door of your car, or touching anything metal.

Lightning is caused by static electricity between the sky and the earth, and that little spark from your electric shock is a very small lightning bolt. (Don't worry, it isn't as big as the picture shows).

The spark is caused by your body containing a static electric charge that is bigger than the static electric charge that the metal object you are touching contains. The metal object thinks that this is unfair and tries to take enough of this charge from you so that it contains the same amount as you. Being a bit too eager to get this static electricity, the metal object will snatch it from you a fraction of a second before you touch it, and the lightning bolt is the transfer of that static electricity between you and the metal object.

Static electricity can be generated by moving on a chair, brushing against desks or walls, or simply walking across an ordinary carpet. Objects can generate static electricity by being handed from person to person, or being wrapped and unwrapped. Clothing made of synthetic fibres is particularly likely to generate static electricity.

Why should it bother me?
Apart from being extremely annoying when you get that electric shock from the door handle, static electricity can cause permanent damage to electronic components if it is allowed to discharge through them. For you to actually feel a static shock, you are discharging somewhere in the region of 3,500 Volts - many times the sort of voltage that can cause damage to some electronic components.

Static damage may not be immediately noticeable, your computer may still work, but it will cause problems later on - your computer may start to fail or do funny things.

Note that your computer is only at risk from static electricity when the top cover is off.

How do I stop static damage?
To stop static damage to your computer when adding extra items (hopefully the only reason the top cover is off), the trick is to have the same static charge as your computer.

All the exposed metal parts of your computer (e.g. case, power supply, etc.) are connected together and in turn connected to 'earth', which basically means no static charge. Touching an exposed bit of metal will discharge your static charge to 'earth' and therefore you will have the same static charge as your computer. As long as you continue to touch an exposed bit of metal, then handling electronic components (e.g. memory, addin cards, etc.) will not damage them. Service engineers wear anti-static wrist straps that connect them to the computer (or a mat that the computer is sitting on) which allows them free movement.