According to Einstein's equation E=mc², energy (E) and matter (m) are interchangeable, meaning that mass can be converted into energy and vice versa. The equation reveals a profound relationship between these fundamental concepts in physics. The "c" represents the speed of light, indicating that even a small amount of mass can be transformed into a tremendous amount of energy due to the squared speed of light factor. This principle underpins various phenomena in nuclear physics and has significant implications in areas such as cosmology and energy production.