Thanks Bibliolept and Trisia!
Yes, perhaps that's the word... I really don't know! There's an example: in tests, teachers will say to their pupils not to write "_______", they'll tell them to answer the questions and don't write stuff that is not relevant! So, is it "background", still?
If you judge something as unimportant, it might be called irrelevant, extraneous, or even pointless. These adjectives, however, imply that you don't think that that material should have been included or that it is of little worth or value.