"Pop" -- meaning to strike, push out, or explode -- is essential in editorial environments or environments where consumers browse information quickly. It implies something that stuns, arrests or stands out visually and inserts itself into the consciousness of the viewer. "Pop" is something that you can test. Designs that rely on the core contrast, repetition, alignment and proximity, or CRAP, principles tend to have a higher visual and psychological register than jumbled, plain and unorganized designs. Thus, strong designs pop, while weak designs fade, if they register at all. Pop is somewhat related to resonance, where an image that pops also has a chance to resonate in the consciousness of the viewer, whereas weak designs are easily forgotten and don't pop out in the viewer's memory.