The soul, according to many religious and philosophical traditions, is a self-aware ethereal substance particular to a unique living being. In these traditions the soul is thought to incorporate the inner essence of each living being, and to be the true basis for sentience. In distinction to spirit which may or may not be eternal, souls are usually (but not always as explained below) considered to be immortal and to exist before their incarnation in flesh.

The concept of the soul has strong links with notions of an afterlife, but opinions may vary wildly, even within a given religion, as to what may happen to the soul after the death of the body. Many within these religions and philosophies see the soul as immaterial, while others consider it to possibly have a material component, and some have even tried to establish the mass (weight) of the soul.

The current English word "soul" may have originated from the Old English sawol. "Sawol" has possible etymological links with a Germanic root from which we also get the word "sea". The old German word is called 'se(u)la', which means: belonging to the sea (ancient Germanic conceptions involved the souls of the unborn and of the dead "living" being part of a medium, similar to water), or perhaps, "living water".

The word "soul" did not exist in the times of Jesus, Socrates or Aristotle, and so the quotations, interpretations and translations of the word "soul" from these sources, means that the word should be handled very carefully. One might go as far as saying that the word "soul", in the sense we use it today, did not exist in Hebrew or Aramaic, but it existed in Greek.Ancient Greeks typically referred to the soul as psyche (as in modern English psychology). Aristotle's works in Latin translation, used the word anima (as in animated), which also means "breath". In the New Testament, the original Greek word used is "Psyche" which in Ancient and Modern Greek means soul.

"For what profit is it to a man if he gains the whole world, and loses his own soul?" (Matthew 16:26)

The Latin root of the related word spirit, like anima, also expresses the idea of "breath". Likewise, the Biblical Hebrew word for 'soul' is nephesh, meaning life, or vital breath.

The various origins and usages demonstrate not only that what people call "soul" today has varied in meaning throughout history, but that the word and concept themselves have changed in their implications.

Source : http://en.wikipedia.org