A gap between how things are and how they need to be. Naming a problem well is most of solving it.
Greek problema (a thing put forward, a question proposed for solution), from proballein (to throw forward): pro- (forward) + ballein (to throw); a problem is, by its own root, something set out in front to be solved.
A gap between how things are and how they need to be, put forward plainly enough to be solved. Naming it well is most of the throwing-forward the word already describes.