What is a supercapacitor?

"A supercapacitor (SC), also called an ultracapacitor, is a high-capacity capacitor with a capacitance value much higher than other capacitors, but with lower voltage limits, that bridges the gap between electrolytic capacitors and rechargeable batteries. It typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors, can accept and deliver charge much faster than batteries, and tolerates many more charge and discharge cycles than rechargeable batteries."
https://en.wikipedia.org/wiki/Supercapacitor

"The supercapacitor, also known as ultracapacitor or double-layer capacitor, differs from a regular capacitor in that it has very high capacitance. A capacitor stores energy by means of a static charge as opposed to an electrochemical reaction. Applying a voltage differential on the positive and negative plates charges the capacitor. This is similar to the buildup of electrical charge when walking on a carpet. Touching an object releases the energy through the finger."
https://batteryuniversity.com/index.php/learn/article/whats_the_role_of_the_supercapacitor

"The biggest commercial supercapacitors made by companies such as Maxwell Technologies® have capacitances rated up to several thousand farads. That still represents only a fraction (maybe 10–20 percent) of the electrical energy you can pack into a battery. But the big advantage of a supercapacitor is that it can store and release energy almost instantly—much more quickly than a battery. That's because a supercapacitor works by building up static electric charges on solids, while a battery relies on charges being produced slowly through chemical reactions, often involving liquids.

You often see batteries and supercapacitors compared in terms of their energy and power."
https://www.explainthatstuff.com/how-supercapacitors-work.html

"A rapidly emerging and increasingly applied technology, ultracapacitors are capable of storing and discharging energy very quickly and effectively. Due to their many benefits, ultracapacitors are currently being utilized in thousands of different applications, and considered in an equally diverse range of future applications."
https://www.maxwell.com/products/ultracapacitors/

"Following Elon Musk’s speech at Cleantech Forum 2011, there has been a lot of interest in supercapacitors and for sure the potential offered by nanotechnologies is keeping high hopes that at some point in the future, supercapacitors might reach a point where they equal the performance of batteries."
https://www.electronicsweekly.com/news/design/will-supercapacitors-supersede-batteries-2018-11/

"Supercapacitors are a type of new energy saving and conversion equipment that is supposed to have the potential of high power density, great circulation feature, rapid discharge-charge, poor self-discharging, safe working, and low cost."
https://www.sciencedirect.com/topics/chemistry/supercapacitors

"Supercapacitors are electronic devices which are used to store extremely large amounts of electrical charge. They are also known as double-layer capacitors or ultracapacitors."
https://eepower.com/capacitor-guide/types/supercapacitor/

"Researchers at the Queensland University of Technology have added another hybrid supercapacitor design to the mix, promising the near-instant charge and discharge of a supercap with vastly improved energy storage on par with NiMH batteries."
https://newatlas.com/energy/qut-hybrid-supercapacitor/