How true does a book need to be to be considered non-fiction?

I believe that a book has to be completely, 100% true to be considered non-fiction. I read fiction to escape to a different world where nothing makes sense, there is magic, and crazy creatures. Quite frankly it doesn't have to make sense, that's its job, to entertain and to make us use our imagination. When I read non-fiction I am looking for factual information, I mostly read non-fiction for school and when I pick up a book that says non-fiction on the cover, I expect the information to be 100% accurate. Mostly I am using non-fiction for reports and projects, if the information is not right I am going to fail the project! I need the information to be right 100% of the time not 95. If I'm reading a book about snakes and the book tells me that a certain breed of snakes can spit acid and fly, first of all im going to believe the book because it is non-fiction, then I am going to get really scared because there are flying snakes that can spit acid! In closing that is why I read non-fiction to get factual, reliable information 100% of the time. Not so I can get a good story that is only 95% true.