Imagery is a catch-all label to describe the complex process of using special word formulas to transfer meanings from the mind of one person to another person in a way that enhances meanings and is based on the very basic structures of the human brain.
You should understand that we use words to try evoke (call up) pictures already in our minds, or to create new ones if we have the skill. Let’s call the part of our minds which deals with pictures the imagination. If we have good imaginations, then we usually have a better-than-basic understanding of what is really going on around us and can develop greater understanding of the world in which we live. We can use what we know to increase our ability to understand new things, or even to “see” things which could never happen: that’s what story-telling is all about.
One special name which is given to the set formulas (the effects and combinations of words which help us to use this quality of imagination) is figure of speech. When an especially strong or vivid picture has been created then we have an image. The group name for these mental pictures is imagery.
These are all words about pictures.
Note that these words (figure, picture, image) refer directly to the non-verbal ideas in our heads. The words are just ways of getting to those images (sorry, it’s very difficult to talk about these things without using circular references). We have to create metaphors such as language tool or device or even instrument to help bring something that exists only in our heads into our real world: we imagine that our mental constructs become something tangible, something we can touch and use with our hands.
All in our imaginations, of course. It is an extraordinary function of the human mind and brain.
You might like to examine my short list of some of these figures of speech here.