Static electricity is the electrical charge associated with lightning, the shock you experience when you touch the doorknob, or when your clothes stick together when they've just come out of the dryer.
Static is caused by the buildup of electric charges when two objects trade some of their electrons from one to the other. The object with the greatest number of electrons has a greater negative charge. Since this occurs without the flow of current, it is called "static".
When the negative charge becomes high enough, any contact with a less negatively, or positively, charged body will cause an extremely rapid, high-current electrical discharge. This is what happens when you cross the room in your socks and touch the doorknob. Your body is negatively charged and the doorknob is positively charged. The negative charge discharges rapidly to the positive charge, bringing the two items back in to electrical balance.