The true nature of Slytherin House is not something that anyone can truly comprehend, for there seems to be only one trait that each and every Slytherin shares, and that is our ability to become invisible. Not invisible in a literal sense, but in a metaphorical one. You see, over the years I have mastered the art of invisibility to the point of perfection. I had to make myself seem invisible even before I begun school, for I had to find some way to avoid my father when he was in one of his rages, especially after mother died. Needless to say it almost always worked.
I am as invisible to the majority of people in Hogwarts, students and teachers alike, as the Thesterals are. I am only seen by those who know I exist in the first place; nobody else would bother to look.
This invisibility has befallen most of us Slytherins, no matter whether we wished for it or not. People like Malfoy show themselves up in front of the rest of the school, and therefore every non-Slytherin presumes that we are all arrogant gits like he is: that, however, is as far from the truth as you could get.
So yes, I know about Slytherin House better even than most other Slytherins, and, to me, to be a Slytherin means to be invisible to most of the world.