A system is time dependent, if its behaviour changes over time based on its past history as well as its current external state. For example, a simple electrical circuit with resistors will always give the same output for the same inputs (time independent behaviour), but if it includes capacitors it can have oscilatiry behaviour that depends on past inputs (time dependence). Time dependence is usually are due to some form of hidden state (such as the levels of charge on capacitors in the electrical circuit) or unobserved state. Many real phenomena, such as human psychology or the stock market exhibit time dependence, for example, if soemone plays a parctical joke your response may well depend on whether you are happy or stressed. Materials wtih time dependent behaviour, such as collections of nanoparticles or biofilms, can be used in reservoir computing to allow it to model complex time dependent phenomena.
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