63 Although some translations have simply “these” or “these people,” since in v. 14 they are described as having eyes “full of an adulteress,” men are in view.
64 Grk “utter darkness of darkness.” Verse 4 speaks of wicked angels presently in “chains of utter darkness,” while the final fate of the false teachers is a darker place still.

In other versions

These are waterless springs and mists driven by a storm. For them the gloom of utter darkness has been reserved.

These people are springs without water and mists driven by a storm. Blackest darkness is reserved for them.

These people are springs without water, mists driven by a storm. The gloom of darkness has been reserved for them.

These people are as useless as dried-up springs or as mist blown away by the wind. They are doomed to blackest darkness.

These people are waterless springs and mists driven by a hurricane, for whom the gloom of darkness has been reserved.

These are wells without water, clouds that are carried with a tempest; to whom the mist of darkness is reserved for ever.

Public Domain