Sequoiadendron giganteum (giant sequoia; also known as giant redwood, Sierra redwood, Sierran redwood, Wellingtonia or simply Big Tree—a nickname used by John Muir) is the sole living species in the genus Sequoiadendron, and one of three species of coniferous trees known as redwoods, classified in the family Cupressaceae in the subfamily Sequoioideae, together with Sequoia sempervirens (coast redwood) and Metasequoia glyptostroboides (dawn redwood). The common use of the name sequoia generally refers to Sequoiadendron giganteum, which occurs naturally only in groves on the western slopes of the Sierra Nevada Mountains of California.

The etymology of the genus name has been presumed—initially in The Yosemite Book by Josiah Whitney in 1868—to be in honor of Sequoyah (1767–1843), who was the inventor of the Cherokee syllabary. An etymological study published in 2012, however, concluded that the name was more likely to have originated from the Latin sequi (meaning to follow) since the number of seeds per cone in the newly-classified genus fell in mathematical sequence with the other four genera in the suborder.