A Venn diagram is when two (or more) circles (or any sort of shape) overlap. That is when the unshared parts of the circles are for different categories... and the overlapped areas are for similarities. Here is an example of use of a Venn diagram: https://www.youtube.com/watch?v=oKgUYokigts
An Euler ("OILER") diagram is like this: https://en.wikipedia.org/wiki/Euler_diagram
(The "Eu" is pronounced "oy" because it was named after a Swiss man named Leohnard Euler, and that's a German-language name.)
Sure you may, and there is no such thing as a Ben diagram.
You know the difference between a Venn diagram and an Euler one?