A dial is a flat surface, circular or rectangular, with numbers or similar markings on it, used for displaying the setting or output of a timepiece, radio, clock, watch, or measuring instrument). There are many instruments used in scientific and industrial applications that use dials with pointers as indicators of a specific physical property, such as pressure and vacuum gauges, fluid-level gauges, voltmeters and ammeters, thermometers and hygrometers, speedometers and tachometers, and indicators). Traditionally, these have been mechanical devices, but with the advent of electronic displays, analog dials are often simulated from digital measurements). The term "dial" may also refer to a movable control knob used to change the settings of the controlled instrument, for example, to change the frequency of the radio, or the desired temperature on a thermostat).

In addition to its use in measuring instruments, the term "dial" can also refer to the face of a sundial, the graduated face of a timepiece, or a device that may be operated to make electrical connections or to regulate the operation of a machine. The term "dial" can also be used as a verb, meaning to manipulate a device (such as a dial) so as to operate, regulate, or select. For example, one can dial a favorite program on the radio or dial the wrong number on the phone.