Pass Through adapters use the mains wiring in the house to connect to each other and spread the wifi network through the house. The pass through bit means you don't lose a socket when they are plugged in.
The link goes to Wifi Mesh devices. These extend the range of a wifi network but each device MUST be in range and receive a reliable wifi signal in order to rebroadcast it. Some Mesh devices can be hard wired - ethernet - if needed to provide wifi in all corners of a house.