Ok so a wave is the physical expression of energy transferring through a medium
Ocean waves are kinetic energy transferring from water molecule to water molecule, sound is high frequency waves moving through a transmissible medium in a way we can perceive as noise, etcetera.
“Light is a wave and a particle” refers to the fact that since photons travel in a probability wave until perceived, they are capable of being their own medium for electromagnetic energy.
This is why light can travel in a vacuum where other wave based phenomenon cannot, light comes with its own medium to travel through the void with.