Āratī is a devotional offering of light, commonly made by moving a flame or lamp before a deity's image, sacred object or other honored presence. The word also names the song of praise frequently sung during that offering. It appears in many Hindu temples and homes, often as part of a wider pūjā, and can be accompanied by bells, music and participation by worshippers.
The central idea is to express reverence through the presentation of light; explanations of what that light symbolizes differ among teachers and traditions. The songs, order, materials and customs are not universal. A publicly available FAQ can explain what āratī is without issuing ritual instructions or claiming that the ceremony must always be performed in one prescribed way.