Also known as a Plato Puss. When you think you recognise a cat but when you run towards it frantically to pet it this "cat" turns out to be some lifeless object. This happens most to cat-happy people who want to see cats everywhere.
You walk down the street and see a cat basking in the sunlight only to find out that it's a black trashbag as you approach it. You have just seen a phantom cat.