I think this word began to be used in the late 1960s or thereabouts. It meant, specifically, a discovery or invention that represented a huge, sudden progress in something that people had been wanting but failing to do for a long time.
Mercury delay lines were reliable but not random-access. Williams tubes were random-access but not reliable. Magnetic core memory was the breakthrough that led to computers as we know them.
Many inventors had been working on incandescent light, but it was Edison who made the breakthrough.