Spirit
That part of a living being that exists before mortal birth, dwells in the physical body during mortality, and exists after death as a separate being until the Resurrection. All living things—mankind, animals, and plants—were spirits before any form of life existed upon the earth (Gen. 2:4–5; Moses 3:4–7). The spirit body looks like the physical body (1 Ne. 11:11; Ether 3:15–16; D&C 77:2; 129). Spirit is matter, but it is more fine or pure than mortal element or matter (D&C 131:7).
Every person is literally a son or a daughter of God, having been born as a spirit to Heavenly Parents before being born to mortal parents on the earth (Heb. 12:9). Each person on earth has an immortal spirit body in addition to a body of flesh and bone. As sometimes defined in scripture, the spirit and the physical body together constitute the soul (Gen. 2:7; D&C 88:15; Moses 3:7, 9, 19; Abr. 5:7). A spirit can live without a physical body, but the physical body cannot live without the spirit (James 2:26). Physical death is the separation of the spirit from the body. In the Resurrection, the spirit is reunited with the same physical body of flesh and bone it possessed as a mortal, with two major differences: they will never be separated again, and the physical body will be immortal and perfected (Alma 11:45; D&C 138:16–17).