Teaching aid is a material which can be used by the teacher while teaching a lesson to enhance the understanding of the student about the subject.
There are many teaching aids. A book, a map. a picture, a computer, a TV, a model or a DVD. Any of them will be a teaching aid. You can select the teaching aid basing on the lesson you are teaching and the level of the students to whom you are teaching the lesson. These teaching aids can be visual aids, audio aids and audio-visual aids.
When you are trying to explain to a student about an animal if you show him a chart in which the picture of the animal is available, it will help the student to understand the animal better. When you are telling him about the various parts of that animal you can mark them on the map and show it to the student so that he will better understand the subject about the animal. Visualising an animal is easy when they see the figure or chart than simply hearing. Then you can show them a chart in which various name of the animal in different languages and other required information is given. The student while hearing you, can read the chart also so that he will have a better understanding of the subject.