A quantum leap is an "abrupt change, sudden increase, or dramatic advance".¹ 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
¹ Merriam-Webster's Collegiate Dictionary, 10th ed., 1999.