| Non-equilibrium systems are characterized by a net energy transfer to the environment. Aging systems pertain to the category of weakly ergodic non-equilibrium systems exhibiting slow relaxational dynamics and strong history dependent effects. In contrast to stationary systems, aging systems are described by two timescales: the waiting time elapsed since the system was set in the non-equilibrium state and the measurement time. The hallmark of aging glassy systems is the violation of the fluctuation-dissipation theorem (FDT) and its two-slopes shape: 1 for short times, where the system is in (local) equilibrium) and x_fdt < 1 for larger times. A characterization of the full spectrum of fluctuations appears key for a satisfactory understanding of the aging state. Over the past years several results about energy fluctuations in non-equilibrium states have been obtained under the heading of fluctuation theorem (FT). They take slightly different forms depending on the non-equilibrium context, but all share the same common feature: they relate probabilities of absorbing and releasing a given amount of energy under non-equilibrium conditions. Recently a fluctuation relation for the aging regime (AFR) of glassy systems has been introduced. Similar to the FDT, it defines a parameter x_af < 1 for the aging regime. Its connection with the parameter x_fdt obtained from Fluctuation Dissipation Theorem was based on numerical evidence. In this talk I will first review the definition of FT and the extension to the agin system deriving the AFR. Then I will show the emergence of the parameter x_af and its meaning. Finally I will discuss the relation between x_af and x_fdt. |