In very simple words, death is the end of life.
For human being, life is the existence of an individual.
In this simple definition another term is necessary in case you want to be explained and that is -life. Did you know that the medical definition further elaborates the two the usual aspects definition, ‘end’ and ‘existence’. Then, in medical science, death is the permanent and irreversible cessation of all vital functions namely the brain function, the respiratory function, and the circulatory or heart function. Certainly, theological or religious part of death is supposed to be important problems comprehensive. Now pay attention please. Integrating the foregoing two aspects, death can be very rationally and scientifically defined as the absolute disappearance of functioning. Consequently, the definition of death for a Muslim my be the absolute disappearance of the functions for the time period in between the two lives -one before death and another after death, I’d say if we integrate the scientific aspect with the description. Islam defines death as a mandatory transitional event in between the ‘life before death’ and ‘life after death’.
In our usual life death is related with the biggest stresses because of the knowledge -death ends.