It is said that a coherent light beam is described by a single wave because all the individual waves add up in phase to produce a single big wave. It is also said that entangled light is described by a single wavefunction. https://qph.is.quoracdn.net/main-qimg-74a1e026576eb278294f9e2ac41996d2?convert_to_webp=true [Broken] These two descriptions are similar and have been a source of confusion for years for me, even for the teachers at my university. They asked me to find out what the difference between light "described by a single wave" and light "described by a single wavefunction" is. From the pictures above, I see no difference between coherence and entanglement, so the Internet won't do for explaining the difference to me. Please do so yourself.