WiFi Direct is a standard that lets two devices connect over WiFi without a shared access point, reaching across roughly tens of metres. It is one of the short range signals proximity payment can use.
The longer version
WiFi Direct allows devices to talk to each other directly, without routing through a common wireless network. It carries the reach people expect from WiFi, on the order of tens of metres, which is longer than a tap and comparable to Bluetooth at the upper end. The Wi-Fi Alliance maintains the standard.
That range makes WiFi Direct useful where presence needs to be detected across a larger space, and where the devices involved already have WiFi radios to hand. It trades the very low power of Bluetooth Low Energy for throughput and reach.
As with the other signals, in the Parousya method WiFi Direct is used only to establish nearness. Even though the standard can move data between devices, the payment does not travel that path. The transaction still routes through a central server.
The Parousya method
WiFi Direct is one of the four signals the Parousya patent names. Even where two devices could link over it directly, the method still routes the transaction through a server, so the devices never pair for payment.