Later during the System Purge, a wraith is seen in a corridor where it is chasing the staff members and killing them. How it kills its victims is not very clear.
It is possible that an urn summons it.
Wraith is a Scottish dialectal word for "ghost," or "spirit". They're said to be death omens who appear to anyone whose death is impending. More or less, the Wraith in the film is represented as an almost normal, common ghost. As such, ghost have appeared in stories since as long as the horror genre has existed.