D&C 19

 After teaching that - 

"...it is not written that there shall be no end to this torment, but it is written endless torment."  (Doctrine and Covenants 19:6)

The Lord teaches - 

"...it is written eternal damnation; wherefore it is more express than other scriptures, that it might work upon the hearts of the children of men..."  (Doctrine and Covenants 19:7)

Eternal damnation is that which will be had if eternal life is not obtained.  Elder Bruce R. McConkie explained - 

“Eternal damnation is the opposite of eternal life, and all those who do not gain eternal life, or exaltation in the highest heaven within the celestial kingdom, are partakers of eternal damnation. Their eternal condemnation is to have limitations imposed upon them so that they cannot progress to the state of godhood and gain a fulness of all things. 

“They ‘remain separately and singly, without exaltation,…to all eternity; and from henceforth are not gods, but are angels of God forever and ever.’ (D&C 132:17.) Their kingdom or progress has an ‘end,’ and they ‘cannot have an increase.’ (D&C 131:4.) Spirit children are denied to them to all eternity, and they inherit ‘the deaths,’ meaning an absence of posterity in the resurrection. (D&C 132:16–25.) 

“They are never redeemed from their spiritual fall and taken back into the full presence and glory of God. Only the obedient are ‘raised in immortality unto eternal life.’ The disobedient, ‘they that believe not,’ are raised in immortality ‘unto eternal damnation; for they cannot be redeemed from their spiritual fall, because they repent not.’ (D&C 29:42–44.)” (Mormon Doctrine, p. 234.)