The circa 1982 joke opening to this definition would go something like this: "Coinbase: a description of the floor of a video arcade after a bomb went off inside it."
But today? What do people use coins for? Smooshing into souvenirs at the zoo? Decorative jar fillers?
Apropos of the growing uselessness of physical money, the real-life definition of "Coinbase" goes something like this: it's the name of a digital currency exchange.
If you cross the border into Canada, they have these little kiosks where you can turn real money into the multi-colored elf-script they use north of the 49th parallel to buy poutine and hockey equipment. Those kiosks are called currency exchanges.
Coinbase is similar to these, only it exists exclusively online and you turn cryptocurrencies (like Bitcoin and Etherium) into other cryptocurrencies, and into traditional currencies, like the U.S. dollar and the recycled water bottles Canadians use to buy moose repellent.