What is a sociopath?

Its someone that has a very weak conscience and doesn't have empathy.

It isn't a medically diagnosed condition, it isn't classified in the DSM (Diagnostic and Statistic Manual of Mental Disorders) so technically doctors don't diagnose people as sociopaths, or psychopaths( they diagnose it as antisocial personality disorder). Psychopaths have no empathy or conscience, sociopaths have a very weak one.

Source: http://www.webmd.com/mental-health/features/sociopath-psychopath-difference