Wafer connectors are very similar to headers. The big difference is these connectors are more suitable as actual connectors as opposed to a place to attach some wires."
Here are the particular differences and similarities:
Wafer connectors are polarized which means you can not plug the mating connector in the wrong way.
The male connector is attached to your PCB board, while the female is attached to a wire cable.
The female connector is crimped on, so no soldering is required (soldering is optional though).
The pin spacing is the same as header connectors, so they are compatible with each other.
Housing are generally made of only plastic parts (some have metal parts), which are assembled with wire and terminal wafer.