What is the difference between periodic and aperiodic signals?

A signal which repeats itself after a specific interval of time is called periodic signal. A signal which does not repeat itself after a specific interval of time is called aperiodic signal.
A signals that repeats its pattern over a period is called periodic signal,

A signal that does not repeats its pattern over a period is called aperiodic signal or non periodic.

Both the Analog and Digital can be periodic or aperiodic. but in data communication periodic analog sigals and aperiodic digital signals are used.