What is a toadstool?

Freya raised her hand "Freya Salvatore. Slytherin." she said before continue with her answer "Its a mushroom, professor." Duh! "Poisonous mushrooms to be exact and it has that umbrella-like cap-and-stem form." Well, that's all she knew about toadstool.

The Slytherin pulled her robes a little tighter. Was it just her or the greenhouse felt colder than the other greenhouse?