35 people died in a huge fireball on 6 May 1937. The freak accident destroyed an entire mode of transportation. It was the Hindenburg disaster and some think it was caused by a build up of static electricity.
On Feb 7, 2008 a disastrous explosion in a sugar mill blew up three silos and covered the destroyed factory with shredded metal that looked like confetti. As farmers and engineers now know, whenever you have a huge amount of a powdered substance in an enclosed space, the risk of a spark and an explosion is great. What would cause such a spark? Static electricity.
Given the horrendous consequences of having stray bits of electricity where they don't belong, understanding and controlling static electricity has been one of the more important issues in many industries. The computer you are using right now for instance could lose its mind if static electricity suddenly appeared in the wrong place. In some electronics manufacturing facilities people have to be careful about what they wear when they are working so as not to cause static electricity to build up and destroy the computer chips.
In nature two electrical sources of charge are found. Negative and positive. In the realm of the physics lab and scientific theory the tiny electron is the source of the negative charge and the huge proton is the source of positive charges.
In chemistry labs and the real world, protons are too heavy and too cumbersome to move easily. Moreover, the protons huddle together with neutrons in the nucleus of an atom and are bound together by something called the strong force. The strong force is much stronger than the force of electricity. In general, in non radioactive materials, it takes something like a nuclear bomb to pry loose a proton. So what we know of as positive charge is not caused by the presence or absence of protons. Rather it is the electrons that have all the credit cards. Only the electrons get to "charge it."
In physics and chemistry the Holy Grail is equilibrium. Given a free choice, the universe prefers to while away the hours doing nothing. For electricity this state of doing nothing is seen when the number of electrons exactly balances the number of protons. If you remove some electrons, the positive charge of the protons will be unshielded and you will see them. Under certain circumstances, you can temporarily get a neutral substance to hold some extra electrons. When this happens we say the substance is negatively charged.
In some compounds and chemicals the electrons more loosely bound than others. Sometimes the electrons are so loosely bound that friction provides all the energy necessary to rip the electrons off of one surface and to cause them to stick to something else.
Now the ripper is negatively charged and the ripped off is positively charged. This is not an equilibrium state. The electrons in the negatively charged item spend all their waking hours looking for something positive so they can jump on it. If nothing positive shows up, they are desperate, so they will find the nearest susceptible surface and induce a relatively positive charge in it.
All items have an electrical state. The ground state is neutral where all positive and negative states have been neutralized. Electrons see any electrically conductive path as a short cut to that ground state. They induce what looks like a positive charge to them in a susceptible surface. Metals which conduct electricity easily, have electrons which can "easily" be persuaded to lean out of way and unshield the protons and their positive charge at the core of the nucleus.
In a cloud of water droplets or flour particles or sugar particles, you have pieces of matter rubbing up on another. Some of these encounters will transfer electrons. If there is a process like a thermal or a rising of warm air that tends to centralize a lot of loose electrons in a particular area, then a great deal of electrical potential can accumulate. The accumulation charge is a little like what happens when you raise a brick into the air. Raise brick a little bit off the ground and drop it and not much happens. Raise the brick 50 feet off the ground and drop it and you could kill man.
Similarly, building electrical charge is like raising a brick some height above the ground. Physicists refer to both situations as gaining potential. In one it's electrical potential. In the other it's gravitational potential. Basically you are storing energy in one form and it will be released in another form.
When a lot of negative electrical charge builds up it begins to see things. If it is close enough to a big positive charge, it will jump to it and we will see cloud to cloud lightning. But the gathering of negative electrical charges don't like one another very much and they are desperate to find mates so almost anything starts to look good to them. In particular, any conductive path almost has to eventually lead to something good. So if the positive charges aren't near enough, or aren't numerous enough, any susceptible surface starts to look close enough to positive to make the electrons jump for it. This is a cloud to ground strike.