What is the difference between analog and digital?

Take a clock for example. A digital clock is one in which you don't have to set. It digitally is set up, and is electronic. An analog clock requires you to set the time, and wind up every so often.

In terms of signal, an analog signal is continuous, and defined through physical measurements. Digital signals are discrete, meaning they are not continuous. 

Take a simple sine wave for example. An analog representation of the wave would be one continuous wave throughout. A digital representation would actually look the same from afar, but if you zoomed in, it would be made up of innumerable samples of varying amplitudes.