This article clarifies the specific application of Albert Einstein's mass-energy equivalence by distinguishing between nuclear and chemical processes. While this fundamental principle underpins the immense energy release in nuclear reactions such as fission and fusion—where a measurable mass defect is directly converted into colossal energy—it is frequently misapplied to common chemical reactions. The paper argues that everyday processes like the burning of cooking gas or a candle, or the operation of a torchlight or tube light, which involve only the rearrangement of atoms and molecules, exhibit a rest mass change so minuscule as to be practically irrelevant. Furthermore, it addresses the misconception that the production of light (luminosity) is a sufficient condition for the principle to apply, emphasizing that the underlying physical mechanism—nuclear change versus chemical bonding—is the decisive factor. This analysis reaffirms the equation's role as a cornerstone of nuclear physics, not a universal descriptor for all energy-releasing events.