A mirror, also known as a looking glass, is an object that reflects an image. Light that bounces off a mirror will show an image of whatever is in front of it, when focused through the lens of the eye or a camera. Mirrors reverse the direction of the image in an equal yet opposite angle from which the light shines upon it. This allows the viewer to see themselves or objects behind them, or even objects that are at an angle from them but out of their field of view, such as around a corner. Natural mirrors have existed since prehistoric times, such as the surface of water, but people have been manufacturing mirrors out of a variety of materials for thousands of years, like stone, metals, and glass. In modern mirrors, metals like silver or aluminium are often used due to their high reflectivity, applied as a thin coating on glass because of its naturally smooth and very hard surface.

आरसा ही एक अशी वस्तू आहे जी प्रकाश प्रतिबिंब अशा प्रकारे प्रतिबिंबित करते की काही प्रकाश तरंगलांबीच्या घटनेच्या प्रकाशात, प्रतिबिंबित प्रकाश मूळ प्रकाशाच्या बऱ्याच किंवा बहुतेक सविस्तर भौतिक वैशिष्ट्ये जपून ठेवतो, ज्याला विशिष्ट प्रतिबिंब म्हणतात.हे इतर प्रकाश परावर्तित वस्तूंपेक्षा भिन्न आहे जे ते सपाट पांढऱ्या रंगासारख्या रंग आणि विखुरलेल्या प्रतिबिंबित प्रकाशाशिवाय इतर मूळ तरंग संकेताचे बरेचसे जतन करीत नाहीत.