They wander like specters on the fringes of the Dreamscape, carefully concealing their emotions and avoiding memories that smell sour or bitter.

There are two words worth mentioning in this sentence.

1.specter

common meaning: sth unpleasant that people are afraid might happen in the future

uncommon ones: a ghost

2.fringe

common meaning: the front part of sb’s hair that is cut so that it hangs over their

uncommon meaning: the outer edge of an area or a group

Well, about the meaning of "specter", the meaning "a ghost" is the common meaning for me, and "sth unpleasant that people are afraid might happen in the future" the uncommon one