Photocatalysts are materials that are activated by light to speed up chemical reactions. The term photocatalyst is often associated with materials such as titanium dioxide, which is commonly used in photocatalytic applications like air purification, wastewater treatment, and self-cleaning surfaces. However, there are several other words that are also used to describe photocatalysts, including photocatalytic materials, photoactive materials, light-activated catalysts, and photoreactors. While these terms differ slightly in meaning, they all refer to materials or processes that utilize light to accelerate chemical reactions. Regardless of the term used, these materials have the potential to revolutionize many industries and make our world cleaner and more sustainable.