The phrase "existing side-by-side" refers to the state of two or more entities coexisting in close proximity to one another, often in harmony or cooperation. Synonyms for this term include "coexisting," "parallel," "adjacent," "neighboring," "concurrent," "simultaneous," "together," "collocated," and "in tandem." These words all convey the idea of things or people existing in the same space or time, whether peacefully or not. "Coexisting" is a broader term that can apply to any kind of relationship, while "parallel" suggests a similarity or connection between the items in question. "Adjacent" and "neighboring" both imply a physical proximity, while "concurrent" and "simultaneous" describe events happening at the same time.