It is possible to explain the concept of tuma in English, but no single word can convey its meaning. Fundamental in the beliefs of Judaism is the understanding that Hashem created everything in the physical world even though Hashem's Nature is purely spiritual and non-physical. The clearest expression of this is in the human soul. Our souls are microcosms of Hashem . This miraculous combination of Pure Spirituality, or G-dliness, with physical nature is the basis of human life.
Death occurs when the tie between spirituality and physicality severs.
The soul returns to its Source, Hashem , and the body remains, much like an empty shell. Without the soul to animate it, the body has lost that which gave it spiritual value. Similarly, the unfertilized egg that is shed during menstruation is also a form of tuma because it could have housed a soul if it had been fertilized. Never again will the minuscule egg have the opportunity to become a human being and carry the amazingly complex human soul. The state of tuma , the state resulting from contact with death, is not a negative thing.