means A facility in the electrical grid where transformers and switchgear step voltage up or down and route power between transmission and distribution lines.

from A straightforward compound: the Latin-derived prefix "sub-" meaning "under" or "subordinate," plus "station," from Latin "statio" (a standing-place or post, ultimately from "stare," to stand). So a substation is literally a subordinate standing-post — a secondary outpost serving a larger system. The word predates electricity, used for any auxiliary branch of a main station (police, railway, telegraph), and it was simply borrowed by the power industry as the grid spread in the late 19th century.