Extraneous
Etymology
From Latin “extraneus,” external or foreign, from “extra,” outside. The same root, through French, gives us “strange.” What is extraneous is, at bottom, a stranger to the matter — it wandered in from elsewhere.
adjective · /ik-STRAY-nee-uhs/
Not belonging to the matter at hand; irrelevant or coming from outside it.
What it names
The material that does not belong — detail that is foreign to the question, cluttering it rather than serving it.
Example
Cut the extraneous detail; the reader needs the decision, not your entire afternoon.
Related idea
What is extraneous does not belong; what is superfluous belongs but is more than needed. Extraneous material is foreign to the point; superfluous material is excess of it.