Thanks, this article gives more information about the basic concept. From what I understand it's a digital wallet hosted in your phone (or another device, could be a card as well maybe?), the wallet must be loaded manually and replenish the same way, and from there the payment can take place completely offline. Sounds similar to concept already in use at small scale (e.g: during university we had our students card used like a small wallet that can be use to pay for meals, snacks and parking through out the city).