A person who seems to have little or no conscience about other people — who lies, uses people, and breaks rules without feeling guilty, and who may be dangerous. That is the everyday meaning, and everyday use is where you will meet it. In real conversation it has drifted a long way: people call a ruthless boss, a cheating ex, or a cold politician 'a sociopath' as a strong insult, meaning 'has no heart and no shame'. Used that way it is an accusation, not a diagnosis, and it can be very unfair. In careful writing the word is treated with more care: doctors today do not use 'sociopath' as an official label at all — the manual they use says 'antisocial personality disorder' — and 'sociopath' and 'psychopath' are popular words, not clinical ones. People often claim a neat difference (a psychopath is born that way, a sociopath is made that way by their life) and you will hear this confidently; the truth is that this split is a popular idea, not an agreed medical fact, and specialists differ. So: understand it, recognise it in films and news, and be slow to aim it at a real person.