I'm undecided about this. Someone who read my ms asked me if I had considered putting in a glossary of terms in my book. Her point was that there are various abbreviations in the story (usually explained, i.e. written out in full the first time used), and also some back story/historical events that she thought could be put into a timeline format. I hadn't considered that at all, to be honest. I explained words or events as I went along (at the risk of avoiding info dumps, I re-wrote many of these sections numerous times..) What do you think? Do you look at glossaries or timelines in books? I must confess I don't always.