As @WBT has thankfully reminded us, this community has not yet created an official on-topic definition for the Help Center. Almost exactly a year ago, @fi12 started this discussion here, too. Lets try to finish it this time!
By now regulars seem to have a pretty good sense of what is and is not on-topic here, but lets formalize this a bit.
I'd like this post to be a place to post on-topic and off-topic items for discussion, one per answer. (I'll provide a few myself, to get discussion started, and provide examples).
Please post both on-topic and off-topic examples, and your suggested wording. And leave comments to discuss and work out the best wording. In a week or so, I, or one of the other mods, can aggregate the responses into the Help Center document.