I challenge you as a community to come up with a valid definition of sociopath. Like the ones you agree with!
I'll begin-- a sociopath is someone who lacks mirror neurons. 
I believe that, unlike a primary psychopath who was born that way, a sociopath (aka secondary psychopath) is someone who was created that way by his or her environment.
A lot of sociopaths have a history of child abuse in some form or another. There is strong indication that this may have caused stunted brain development, which in turn created many of their sociopathic traits.
I don't agree with the term sociopathy at all. It should be put to rest.
There was a time when we realized some people are different, and they were called psychopaths. Sure, at first all weirdos were called psychopaths but it didn't take long before the word was used as today, someone born with antisocial traits.
Renaming it sociopathy was cowardly, the word psychopath meant what it was and it could offend. The view had changed and it was now believed you couldn't be born a certain way, everyone was born the same and therefore it wasn't the poor sociopath's fault he was one. But it actually meant the same thing, it just questioned the roots of psychopathy.
These days we're back to calling psychopaths psychopaths. There aren't many researchers actually using the term sociopath anymore. The term is kept alive by poor souls on the Internet thinking it means secondary psychopath. But when the term sociopathy was coined it was believed all psychopaths were born normal.
Psychopath = sociopath.
But not to go OT too much... a sociopath/psychopath is someone with immature emotion, who reacts like a baby where there is no happy but only pleasure, and no sad and upset, just a mixture of negative angryish emotion.