A movement through stages in order. Also a sequence of chords — both are steps that imply where they are going.
Latin progressio (a going forward, an advance), from progredi: pro- (forward) + gradi (to step); the same root gives grade and gradient, all built on the image of a step taken.
A movement through stages taken in order, whether the stages are a plan or a sequence of chords. Both readings share the same root image: a series of steps, each implying where the next one falls.