There's no such thing as a real apple.

Most of us had those silly kid's books with a picture for every letter of the alphabet; almost always, "A" is represented by "apple" - generally a picture of a bright red shiny apple, sometimes including a happy-faced worm poking out of it. That picture - or some other like it - became the foundation of the concept of "apple" we associate with the word "apple" for the rest of our lives. Over the years, we've added to it, modified it slightly. We've encountered real apples and other pictures, and so the mental image gets a little distorted from that original. However, when we think "apple", we see the picture.

The problem is, it doesn't exist. No apple ever looked like that. Even if your mental image is of the last physical apple you ate, your image is incomplete as well as tainted by other memories.

Simply put, the image in your head - the concept of a "real apple" - doesn't exist, and any real apple that does exist won't exactly match the image in your head. So, there's no such thing as a real apple - just the approximations of "apple" to varying degrees.