simply, a signal is a set of information or it is also defined as any function in general of time that carries the information. eg: music, picture, speech etc.
continuous and discrete time signal
A signal is said to be a continuous if it can be defined for all possible real value of the time variable. such that speech , video camera etc. A signal is said to be a discrete time if it can be defined for set of discrete value of time variable. such that stock market daily average, monthly sales of a corporation etc.
analog and digital signal
a signal whose amplitude can take on any value in continuous range( infinite number of values) is known as analog signal. such that atmospheric temperature, pressure, voice etc. a signal whose amplitude can take only finite number of values is known as digital signal. such that computer output , written message etc.
advantage of digital system
- Easy to store and manipulate (music compression and decompression).
- can be proceed and transmitted more effciently