The formal end of a piece of work, whether because it finished or because it was stopped early. In iterative delivery it is a decision rather than an arrival.
Closure covers four separate jobs that do not finish together: transferring the delivery to whoever will run it, dispersing the team, completing the administration, and capturing what the organisation should do differently next time. The last two are the ones that fail, because neither has a natural owner and both fall due after the team that could have done them has moved on. Predictive work is forced into closure by reaching its final deliverable; iterative work is not, so the decision has to be made deliberately. Work that merely stops being funded has been abandoned rather than closed.
Where this comes up
Predictive work gets an ending for free, the day the thing is handed over. Iterative work has to manufacture one, which is why so much of it never formally ends at all.
Three types, separated by one variable: how much authority the office holds. Supportive advises, controlling requires, directive runs the work. Level is a second axis and a different question.