What better way to express your wealth than to literally wear your credit card around and use it to buy more things to wear and adorn your life? Visa would very much like it if you did that, so it's made an NFC-enabled ring that's able to make purchase at terminals that accept contactless payments. The idea is to make it as quick and easy as possible to make a payment; no need to pull our your credit card or phone — you can just tap your ring to the terminal.
Other smart rings have tried this before
The idea isn't totally novel. Plenty of smart rings have passed through Kickstarter claiming to offer contactless payments over NFC. That said, Visa says this is the first ring "backed by a Visa account," so it's possible those others never quite got the support they needed.
Visa is giving out its payments ring to 45 athletes heading to the Rio 2016 Olympics. It doesn't say whether the ring will ever be offered wider than that, so this may well be a tech demo just to show what wireless payments can do. That's probably fine. It's easy enough for small gadgets to enable wireless payments, so if Visa allows it, quite a few other wearables will be able to offer this same functionality.