When building models or algorithms, we construct a space which contains the expected behavior and tailor our models to that space. Edge cases can occur in the real world, existing at or past the boundary of what’s expected and what we prepared for. Edge cases can also be unique combinations of variables that interact in a way that we didn’t think of (this is often called a corner case), or variables we didn’t consider entirely.
Humans with unique circumstances or experiences can become living edge cases.