マッシュルーム is the transliteration of the English word “mushroom.”
Some people might be saying “so what?”
In Japanese, マッシュルーム refers to the edible “button mushroom” or “champagne mushroom” – the kind shown in the top right section of the picture. All the other mushrooms in the picture are キノコ but not マッシュルーム!
“Edible mushroom” is called 食用（しょくよう）キノコ in general and キノコ part is very often written in Katakana (the kanji for it is 茸) although it is a Japanese word. Some fungi are also called キノコ.
The Japanese cuisine uses lots of different mushrooms and each has a name. Probably the most famous kind is 椎茸（しいたけ）. You may have heard of えのき茸（だけ） as well. In these names the kanji 茸 is pronounced たけ or だけ.
“Poisonous mushrooms” are called 毒（どく）キノコ in general.
By the way, when I first came to Australia, I was astonished to see people eating マッシュルーム raw! Because until then, I had been told mushrooms need to be cooked before eating. Some edible キノコ in Japan can cause problems if you eat them raw, so make sure you cook them first!
