Science, Tech, Math › Science Quantum Definition in Physics and Chemistry What Quantum Really Means in Science Share Flipboard Email Print Quantum entanglement occurs when particles become linked across space and time, interacting even though separated by a distance. MARK GARLICK/SCIENCE PHOTO LIBRARY / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated August 09, 2019 In physics and chemistry, a quantum is a discrete packet of energy or matter. The term quantum also means the minimum value of a physical property involved in an interaction. The plural of quantum is quanta. Key Takeaways: Quantum Definition In chemistry and physics, quantum refers to a single packet of matter or energy.In practical use, it refers to the minimum amount of energy required for a change or the minimum value of any physical property in an interaction.Quantum is the singular form of the word. Quanta is the plural form of the term. For example: the quantum of charge is the charge of an electron. Electric charge can only increase or decrease by discrete energy levels. So, there is no half-charge. A photon is a single quantum of light. Light and other electromagnetic energy is absorbed or emitted in quanta or packets. The word quantum comes from the Latin word quantus, which means "how great." The word came into use before the year 1900, in reference to quantum satis in medicine, which means "the amount which is sufficient". Misuse of Term The word quantum is often mis-used as an adjective to mean the opposite of its definition or in an inappropriate context. For example, the term "quantum mysticism" implies a correlation between quantum mechanics and parapsychology that has not been supported by empirical data. The phase "quantum leap" is used to suggest a large change, while the definition of quantum is that the change is the minimum amount possible.