Diffraction is a wave phenomenon that occurs when waves encounter an obstacle or pass through a narrow opening. Instead of continuing in a straight line, the waves bend and spread out, especially when the size of the opening or obstacle is comparable to the wavelength of the wave.
This effect is most noticeable with light, sound, and water waves. For example, you can hear someone speaking around a corner (sound diffraction), or see a blurry edge of a shadow (light diffraction). The amount of diffraction increases when the wavelength is larger relative to the size of the gap or object.
Diffraction is key to understanding various wave behaviors in physics and is essential in technologies like X-ray crystallography, optical instruments, and radio communication. It also supports the idea that light and other forms of radiation behave as waves.