The document discusses discrete-time control systems. It defines discrete-time systems as dynamic systems where one or more variables are sampled at certain time intervals, so they work with discrete or digital signals. It presents a basic block diagram model of a discrete-time control system and explains how the z-transform can be used to obtain the discrete-time transfer function by analogy with the Laplace transform for continuous systems. Finally, it gives an example model of a control system and derives the open-loop and closed-loop transfer functions from the model.