“The revelations also speak of the day when the Lord’s vineyard shall be burned, a day when the righteous shall be preserved, but one in which every corruptible thing shall be consumed, in which the elements shall melt with fervent heat and all things shall become new. (D. & C. 101:23–25; Mal. 3; 4.) That is the day in which the tares shall be burned (D. & C. 101:66), in which the Lord will ‘consume the wicked with unquenchable fire.’ (D. & C. 63:32–34, 54; Matt. 3:12; Luke 3:17.) Finally, all those who suffer the second death shall suffer the vengeance of eternal fire (D. & C. 63:17; 76:44, 105); their torment shall be ‘as a lake of fire and brimstone, whose flame ascendeth up forever and ever.’ (Alma 12:17.)”
(Bruce R. McConkie, Mormon Doctrine, p. 280).
In one sense this fire is figurative because it does not bring an end to the existence of the wicked individuals; they go on living in eternity. But the fire is real in the sense that it causes actual mental pain and remorse. Doctrine and Covenants 19:1–20 also discusses the effects of this suffering.