??

This is just my take on it, but I understood it to be the piece of Voldemort's soul that had been residing in Harry ~ thus making him a horcrux.

I agree that I thought it was the piece of Voldemort's soul.

yeah i agree that it was part of voldemorts soul, a horcrux, that was broken off and was part of harry when voldemort tried to kill him when he was one years old. and when harry's soul went to king's cross (kinda like limbo or where u go before u go into the light) voldemorts soul was the one that went onto whatever life is out there, and that's why Harry's soul got to keep living.
at least that's how i see it.

It actually wasn't a boy. As I understood it, it was a piece of Voldemort's soul in the form of a baby lying under a bench.

When Harry returned from King's Cross, Voldemort was recovering from some kind of faint. Later, Harry says that he's seen what's in store for Voldemort.

I believe that the crying thing under the bench is all that's left of Voldemort's soul, which went to King's Cross and back with Harry. We are given a chance to see how pitiful and wretched Voldemort's soul has become, the price he has paid for his evil ways, the end that awaits him if he will not repent and have his soul healed.

I agree with you but I can't put it as well, so thank you for putting better than me.

it was Voldemort's 7th part of his soul. When i first heard of the Horcruxes, I kinda thought that it was Harry that had it, but when the characters thought it was the snake, I kinda thought that too. Harry was an unintentional Horcrux.

It is the piece of Voldemort's soul that still resided in Voldemort before he died; it is J K Rowling's mastery that she has left it unnamed, leaving us to wonder, and eventually figure it out. It also amplifies the untouchability factor of that "thing", don't you think?

As has already been stated it was the broken , abused, shriveled being of what was left of Voldemort's soul that had been placed in Harry. When the "Child" was separated from Harry it signified the fact that he had separated himself from the Horcrux and had severed his connection to Voldemort