The factory interior fuse block includes +12V sources for accessories. This includes illumination power (ie. fog lamps, etc), ignition-switched power (radar detector, dash-cam, etc), and constant power.
This factory connector and terminal allows a secure method of powering these accessories. The connector clips in to the fuse block, eliminating the possibility of a standard spade style terminal from popping off.
Installation requires an open barrel crimping tool, such as this one.