A diagram is a graphic designed to communicate information. This can appear in a variety of ways from the symbol-based "Don't Walk" signs you see on the street every day, to the pie charts that break down cost percentages in the business world. Diagrams provide an alternative means for people to connect with information and process its significance.
Diagrams offer a way for your audience or classroom to visually conceptualize the material and engage with it in a way that isn't necessary possible with lecture alone. Certain types of diagrams, such as Venn Diagrams, show the interrelation of concepts by placing interrelated words in overlapping bubbles. This can help students understand lessons that may seem too complicated when communicated in a purely lecture-based teaching situation.
A diagram is essentially a picture that communicates information. You can often explain statistical data and other important information, like how a particular system functions, quickly and with less of a strain on resources. Using a diagram is more effective than a narrative-based process. This is especially important in the business world where information constantly disseminates and the need for accuracy, speed and comprehension is paramount.
In the bright and shiny world of desktop publishing, colorful presentations that catch the eye can mean the difference between listeners absorbing your information or turning your concept down. A presentation depending heavily on diagrams can both maintain your listener's attention by giving them something engaging to look at and by allowing them to absorb the information in consumable, memorable chunks. A diagram is also helpful in distilling your lesson plan or presentation into simple concepts, which allows your listeners or students to quickly comprehend your outline.