What Is a Signal？ A signal is formally defined as a function of one or more variables that conveys information on the nature of a physical phenomenon. When the function depends on a single variable, the signal is said to be one dimensional. When the function depends on two or more variables,the signal is said to be multidimensional.What Is a Signal? • A signal is formally defined as a function of one or more variables that conveys information on the nature of a physical phenomenon. • When the function depends on a single variable, the signal is said to be one dimensional. • When the function depends on two or more variables, the signal is said to be multidimensional