Incense is a type of biotic material that when burned releases a fragrant smoke. It is used by a number of races, including humans, Vulcan, and Klingons, for a variety of purposes. These purposes include for simple aesthetic reasons, as well as for theraputic purposes, in meditation, and for ceremonies.
In 2257, while Sarek was meditating on a Vulcan shoreline, his wife Amanda Grayson brought him a bowl full of burning incense to aid him in his meditations. (DIS: "Such Sweet Sorrow")
The Klingon Mauk-to'Vor ritual required the use of adanji incense, which had to be real and not replicated. The fact that Quark had sold adanji incense to Worf was enough to alert Jadzia Dax that Work was planning to carry out Mauk-to'Vor for his brother Kurn. (DS9: "Sons of Mogh")