A) A continuous electrical signal that carries information in the form of variable physical values, such as amplitude or frequency modulation.

b) A signal which moves through a continuous range of settings or levels.

c) An adjective describing any signal that varies continuously as opposed to a digital signal that contains discrete levels representing the binary digits 0 and 1.

d) A signal that is an analogy of a physical process and is continuously variable, rather than discrete. See also Digitization.