The word "后援" is formed by combining two conceptual characters: "后" (hòu), meaning "behind" or "rear", and "援" (yuán), meaning "to aid" or "to support". Together, they create a spatial metaphor where support is visualized as coming from behind, like reinforcements held in reserve or a foundation backing up the front line, thus conceptually merging into the single idea of "backup" or "reinforcements".