MTA (Mass Termination Assembly) connectors from TE Connectivity / AMP, work by squeezing individual wires into slots in the back of the contacts. This is done with a special tool. The slightly narrower slot slices through the insulation and squeezes tightly into the conductor. Creating a gas-tight connection between freshly-scraped metal surfaces. It is a reliable and quick way of connecting as long as wire of the correct gauge is used. Attempting to remove an MTA connector by pulling on the wires will instead pull the wires out of the back of the housing. The header can be fitted with an optional dust cover. This fits over the top of the housing keeping it tidy and preventing the wires from being pulled out.
MTA housings mate with MTA headers on the PCB. The MTA headers look very similar to the Molex KK connector ones but are not the same. Do not try an force an MTA housing onto a KK header or vice versa.