A vignette (vihn-yet) is like a little story that helps people imagine what might happen in different situations.
Say you and your friend are playing with some toys, and your friend takes your favorite toy without asking. Your mom might ask you how you feel about what happened, to see how you understand what's going on.
If your mom wanted to use a vignette, she might tell you a story first. She could say something like, "Imagine if you had a toy car that was your very favorite. You loved to play with it all the time. But one day when you weren't looking, your friend took it without asking. How do you think you would feel about that?"
By telling you a story that's kind of like what you're dealing with, your mom is helping you understand the situation better. Vignettes are a way for people to think about how they might act or react in different situations, without actually having to live through those situations.