I think a prompt is everything that motivates you.
It can be anything, and it doesn't have to have anything to do with what you go on to create, it's simply a catalyst. Maybe that's what this semi-regular column should be called: catalyst.
Whether you're writing a poem or a polemic, if you're noodling on a novel or stewing over the next step in a short story, sometimes a lyric is enough to propel you forward – I know lyrics can often help me as I walk around grumbling to myself about a plot point – and speaking of point, mine is just this:
Oh ye! Look upon this image of an exploding apple, a lighted sign at night, at the fulsome words cathedral and matches burning, and let any or all of these clear your brain or fill it, whatever you need right now to help you write.
P.S. As ever, we have to moderate anything you share in the comments because o' bots, but that's one of the purposes of those comments: share whatever this brought out for you!