Picture this: imagery is a noun to describe the way things or ideas seem in your mind or in art or literature.
Imagery comes from image and originally referred to physical things like statues. Now it is more often used of an artist's or writer's depictions ("Shakespeare's imagery shows a wide knowledge of the world") or of the pictures of the world in someone's mind. Think of imagery as being the stockpile of your imagination. If the imagery in your dreams is a little scary, it might be time to stop eating those spicy meatball sandwiches right before bedtime.