Models, graphs, charts, pictures....any tool that helps the learning process is considered a visual aide.. As long as you can see it and it helps students learn easier, Its a visual aide.
Visual aid are making slides and projecting them onto a screen, at various sizes, it depends on the size of the audience. They are about getting the bullet points over, the core of what is being taught. Visual adis, we might use in science - tactile examples are essential and seeing is one of our main accessing systems to knowledge, we see it, and for some people that's there preferential accessing system. We are also Auditory and often visual aids are combined with explanatation and well, we use all the senses in different preferential order. Visual aids simplify the message that is being taught and from there good questions can arise and you can store the picture of the words or the graph of whatever was shown in your mind ready to access at another time.