What are de Broglie waves?
Louis de Broglie extended the notion of wave motion from light to other particles, such as electrons. It is possible to calculate a de Broglie wavelength for anything, including an elephant!
The formula is
If you do the calculation, you will find out that the de Broglie wavelength for big objects like an elephant or a tennis ball is immeasurably tiny. It is only for very tiny objects like electrons that the concept really has much significance.