Memory

Memory-less system

A system is memory less if for any $ t_0 $, the output at $ t_0 $: $ y(t_0) $ depends only on the input at $ t_0 $ (not at past or future time).

System with memory

A system is with memory if for any $ t_0 $, the output at $ t_0 $: $ y(t_0) $ depends on the input at past or future time.