Electricity is a fundamental form of energy occurring naturally (as in lightning) or produced artificially, and results from the motion of electrically charged particles of matter. These charges are either neutral, positive, or negative. Electricity is concerned with the positively charged particles, such as protons, that repel one another and the negatively charged particles, such as electrons, that also repel one another. Negative and positive particles, however, attract each other. This behavior may be summarized as follows: Like charges repel, and unlike charges attract.