Anti-matter is matter that has counter properties to “normal” physical matter. In normal matter, an electron is negatively charged. So, anti-matter electrons and protons have the opposite set of electrical charges to normal matter. Therefore, in anti-matter a proton is negatively charged (called a "anti-proton," and an electron is positively charged (called a "positron"). Theoretically, when equal amounts of matter and anti-matter are combined, complete conversion to energy is the result.