Superposition in sense of linear combination of quantum states. For example 2-state superposition is qubit. If you think about systems can be in superposition

Superposition in sense of linear combination of quantum states. For example 2-state superposition is qubit. If you think about systems can be in superposition only relative to one another. For example in double slit experiment light is in superposition relative to us, but not relative to photon from other slit. Or maybe photon in one slit does not exist in timeline of photon from other slit? I don't know :)