A quantum leap is an "abrupt change, sudden increase, or dramatic advance".? The term dates back to 1956.
The word Quantum (from Latin quantus, "how much?") dates back to the 16th century, meaning a quantity or amount. Today, the word is strongly associated with quantum mechanics, where it means an indivisible quantity or amount.
It is sometimes said that a phrase such as a quantum leap in technology is inappropriate, because "quantum" supposedly means "small" in quantum mechanics. So a quantum leap in technology would be a small advance. However, "quantum" does not actually mean "small" in quantum mechanics; it means "discrete", "indivisible", or "all-at-once". A quantum leap in technology would be an advance that happens all at once, rather than gradually over time. If advances are classified as either evolutionary or revolutionary, then a quantum leap in technology would be the latter.
References
? Merriam-Webster's Collegiate Dictionary, 10th ed., 1999.