The claim is that there are some parts on some organisms, such as the flagellum on some bacteria, that could not have come about through a successive process where more and more "components" of the whole structure were added over passing generations.
Gotcha thanks. that's what I thought you meant after having watched something on ID. The bacterial flagellum being the explanation/evidence of ID.
Quick -- what's the difference between the "irreducibly complex" flagellum and Piltdown Man? Give up? When scientists discovered Piltdown Man was a hoax, they walked away from it.