Signal and System

In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal.Signals can be categorized in various ways. The most common distinction is between Discrete and Continuous spaces that the functions are defined over, for example discrete and continuous time domains.Discrete-time signals are often referred to as time series in other fields. Continuous-time signals are often referred to as continuous signals even when the signal functions are not continuous; an example is a square-wave signal.