Incense was a type of biotic material that when burned releases a fragrant smoke. It was used by a number of races, including Bajorans, Humans, Vulcans, and Klingons, for a variety of purposes. These purposes included simple aesthetic reasons, for therapeutic purposes, in meditation, and for religious 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 Worf was planning to carry out Mauk-to'Vor for his brother Kurn. (DS9: "Sons of Mogh")
In 2373, Benjamin Sisko had a vision of B'hala on the eve of the Peldor Festival. It was so real that he could smell the burning bateret leaves and taste the incense on the wind. (DS9: "Rapture")
In 2376, Neelix offered Tuvok some Vulcan incense. (VOY: "Riddles")
In 2380, Ensign D'Vana Tendi obtained some incense, among her various attempts to help Lieutenant jg O'Connor ascend. (LD: "Moist Vessel")