The word caustics has several meanings depending upon the context in which it is used:

• In Greek language, from which this word originates, caustics means "to burn" or "burning".

• In optics, a caustic is a bundle of light rays. For example a caustic effect may be seen when light refracts or reflects through some refractive or reflective material, to create a more focused, stronger light on the final location. Such amplification, especially of sunlight, can burn -- hence the name. A common situation when caustics are visible is when some light points on glass. There is a shadow behind the glass, but also there is a stronger light spot. Nowadays, almost every advanced rendering system supports caustics. Some of them even support volumetric caustics. This is accomplished by raytracing the possible paths of the light beam through the glass, accounting for the refraction, reflection, etc. Reference: Max Born and Emil Wolf, Optics.

• In differential geometry a caustic is the envelope of rays either reflected or refracted by a manifold. It is related to the optical concept of caustics.

• In chemistry a caustic substance is one that 'eats away' or chemically burns other materials. Concentrated solutions of strong bases, such as the hydroxides of alkali metals and alkaline earth metals, are usually caustic. Caustic substances, such as drain cleaners, are harmful to living tissue.

• Caustic is also used as an abbreviation for "caustic soda", a common name for chemical compound sodium hydroxide (NaOH).