My definition- People who don't understand and are stuck in the past. People think it is unnatural to love or have sex with the member of opposite sex. Love is love and it shouldn't matter who the person is. Women are beautiful, wonderful. Men are handsome, amazing. Why does it matter what gender they are? They aren't any different so why is it so hard for some people to treat them like the human beings they are?
Because if you are only attracted to the oposite sex, than you dont understand how someone could be attracted to the same sex. People fear what they do not understand. They also choose to not agree with something if the yfeel the oposite about it.
In short, its ignorance. Ignorance in knowledge, and ignorance in action.