A toad's eye view of a toadstool

The Shaggy Parasol Chlorophyllum rhacodes is an impressive mushroom. Or is it a toadstool? It's not at all clear to me what the essential difference is between a toadstool and a mushroom. One definition might be that if it is good to eat then it is a mushroom whilst if it makes you ill, or even kills you, then it is a toadstool. But that leaves us with a huge number of fungal fruiting bodies that are inedible yet harmless.

The bigger the better!