is what causes those little sparks when you rub a part of your body against something like a carpet or a balloon
and touch a metallic object. The buildup of voltage on your body when you do so is on the magnitude of kilovolts, but static electricity is not dangerous at all. It's called static
because there is no current involved with the transfer of charges from surface to surface. The charges flow naturally, however, so static electricity is not truly "static".
When two surfaces rub against each other, there will be some transfer of charge. In the case of static electricity they will stay because they won't conduct back to their "homes". Electrons go from one surface to another as a result of electrical forces, not friction. The more surface area exposed, though, the more chances electrons have to form bonds and be transferred. Which material gives up its electrons and which will take them depends on a property called triboelectricity.
When this is done, there are extra electrons on one surface, giving it a net negative electrical charge. The other surface, which donated the electrons, has a net positive electrical charge. Since there are so many like charges on the surface, the surface is acting almost like a capacitor. When you touch a Van de Graaff generator, like charges build up in your body. Since opposites attract and likes repel, the hairs on your head are trying to get as far away from each other as possible by standing on end.
Those extra electrons will bleed off over time, but they can be released instantly through contact with a conductor. Metal has a high conductance. When a statically charged surface and a conductor come together, there is an instantaneous transfer of electrons, causing a small spark.
There is a lot of voltage involved in static electricity, but it is nothing to worry about. It's not voltage, but power that can cause damage . Power is equal to voltage times current. Since there is almost no current involved here, the amount of power that is produced is very low. Even if you were to build up 10,000 volts on a surface through static electricity, a current of 0.1 milliampere would produce only one watt of power.