What was does Einstein's theory of relativity state and what does each letter mean?

Einstein's theory of relativity consists of two parts: special relativity and general relativity. Special relativity, introduced in 1905, asserts that the laws of physics are the same for all observers in uniform motion and that the speed of light is constant in a vacuum for all observers, leading to the famous equation (E=mc^2), where (E) is energy, (m) is mass, and (c) is the speed of light. General relativity, published in 1915, describes gravity as the curvature of spacetime caused by mass, altering our understanding of gravitational forces. Together, these theories revolutionized our comprehension of space, time, and gravity.