The Rayleigh Criterion is a principle in optics that defines the minimum angular separation at which two point sources of light can be distinguished as separate entities. According to this criterion, two sources are resolvable if the central maximum of one source's diffraction pattern coincides with the first minimum of the other. This concept is crucial in fields like astronomy and microscopy, where clarity and detail are essential. This criterion is named after the British scientist Lord Rayleigh, who formulated it in the 19th century. It highlights the limitations of optical systems, such as telescopes and microscopes, in resolving fine details due to the wave nature of light. Understanding the Rayleigh Criterion helps in designing better optical instruments and improving image quality.