In signal processing and related disciplines, aliasing is an effect that causes different signals to become indistinguishable (or aliases of one another) when sampled. It also often refers to the distortion or artifact that results when a signal reconstructed from samples is different from the original continuous signal.
Please give me an example of this phenomenon that I can understand as a layman.
An example of aliasing that easy to understand as a layman is the 'wagon wheel effect'. You've probably seen the wagon wheel effect when watching a movie or tv show and the wheels of a car appear to be spinning backwards even as the car moves forwards. This is an effect of aliasing. This occurs because the sampling rate of the film is not adequate to capture the frequency of the signal (the frequency that the tires are spinning forwards) and the signal becomes indistinguishable from another signal (a frequency of the tires spinning backwards). As an example of how this happens imagine that the camera's sampling rate allows it to record an image frame at about 90% of the frequency that the tires are spinning. That is, the tire is spinning fast enough that it rotates 90% around in between each picture the camera can take. In this case, the wheel will look like its rotated backwards by 10% of a rotation on each image. When you put these images together in a film, the tires will appear to be rotating backwards.