A venn diagram is ,(as the other person said), an illustration that usually has 2-3 circles, and maybe four at most. A Venn Diagram is useful when grouping things together, sorting, or adding on alike things to one another. When having two circles, they would be intertwined together in the middle. The two main parts of the circles would be the things you chose to put in there. Maybe, pros and cons, or different animals like dogs and cats. The middle between the two circles would be where the two things/objects of your choice are alike, or maybe something they share.