That piece of meat that sometimes hangs, soft and pliable; sometimes bulges and rises a bit; sometimes hardens and stands like a soldier at attention...it defines you. In infancy. In the womb. It defines you. It labels you male.
Initially, it means nothing more to you than the way you take a piss. Mom or dad have taught you how to stand and aim, how to clear the last dribble from the hose (you do know how to do that, right?), how to shake off the last drop before you stuff it back into your pants.
Then, one day, even as young as four or five years of age, you discover it gets a bit hard. You wonder why it does that. If your dad is a cool dad, he explains the phenomenon to you. It needs a fresh supply of blood to stay healthy.
Then, probably around eight or nine, you find out that, if you touch it, play with it, it gets even harder and it feels really nice when you do that.
Then, that second bath of testosterone starts to kick in, hair begins to grow around it. It gets hard at the drop of a hat. If your dad is not a cool dad, you wake up one night drenched in some semi-thick, sticky wetness you know nothing about. You just know you dreamt something - you can't remember what it was, really - and you feel...strange but good. A little shaky, your breathing rapidly, but, still, it feels...nice. Yet, you're scared - what happened - is there something wrong 'down there' in that place you've been told is dirty, private; that thing 'nice people' don't talk about; that thing you're supposed to keep hidden from view.
After a while - weeks, maybe months, you discover you can make it get hard, it feels really, really good to play with it, to tease it. And that 'thick piss' comes out and it feels so awesome when it does. You've stumbled across your cock and it's amazing ability to make you feel good.
You dare to talk to a buddy about what you've experienced. He says, "Yeah, mine does it too." Or some of the other guys in school start to make open comments; you hear words like boner, hard-on, jizz, jack off. Or maybe you've dared to share the experience with one of your buddies.
Now, your cock - your manhood - defines you as a man, though you've not quite reached a level of mental maturity to be accepted as such.
Now what does your cock mean to you?