IN THIS PAPER, WE PROVIDE AN EXPRESSION FOR THE ENTROPY OF THE RESIDUAL LIFETIME OF ACoherent System, ESPECIALLY AN I -OUT-OF- N System, WHEN ALL COMPONENTS OF THE SystemARE ALIVE AT TIME T. VARIOUS PROPERTIES OF THE PROPOSED ENTROPY ARE DISCUSSED. SOMEPARTIAL ORDERING RESULTS AMONG THE System RESIDUAL LIFETIMES IN TERMS OF THEIR ENTROPIESARE ALSO OBTAINED.