Subatomic particles are waves of probability.

It is worth looking up the Wave Equation and meditating on the fact that waves are solutions to a problem/set of conditions around conservation of energy.

It is an open ended definition not one that points out a discrete thing.

Surface waves for example such as Rayleigh Waves and Love Waves are solutions to the conservation of energy of a wave that cannot propagate past a free surface and thus energy in that direction must be conserved some other way through the solution of a surface wave.

https://visualpde.com/basic-pdes/wave-equation.html

https://visualpde.com/sim/?preset=waveEquation

^this is really fun I found it by accident because of this post.

https://en.wikipedia.org/wiki/Wave_equation

The second derivative (the acceleration) of energy in terms of time t is equal to a constant multiplied by the second derivative of energy in terms of distance x...

It suggests a basic back and forth transformation or equivalence at the heart of it, a wave is a relation embodied within physical constraints.