I guess if we are truely honest with ourselves, few of us could walk around in broad daylight and not be read. (For those of you who are lucky enough to be blessed with really feminine features and body; good for you!)
For me "passing" means being confident within myself that I look as feminine as it is possible for me to achieve. Having said that, as I am firmly closeted very few people have had the chance to critically tell me to what extent I have achieved that aspiration!