Okay kiddo, so imagine you have a big group of things like toys or foods. The criterion of dissimilarity is a way to figure out which things are different from each other.
Let's say you have a bunch of toys like blocks, dolls, and cars. The criterion of dissimilarity would help you figure out that blocks and dolls are different because they look and feel different. Cars and dolls are also different because cars are made for zooming around while dolls are made for imaginative play.
Sometimes the criterion of dissimilarity is used when we want to group things together or separate them out. It helps us understand what makes things unique and special.
So, in summary, the criterion of dissimilarity is a way to find differences between things and figure out how they are unique.