Signals
When data is sent over physical medium, it needs to be first converted into electromagnetic signals. Data itself can be analog such as human voice, or digital such as file on the disk.Both analog and digital data can be represented in digital or analog signals.
Digital Signals
Digital signals are discrete in nature and represent sequence of voltage pulses. Digital signals are used within the circuitry of a computer system.
Analog Signals
Analog signals are in continuous wave form in nature and represented by continuous electromagnetic waves.