You mean the piece of extruded aluinium?
It's just part of the rip fence. It can be used as-is to rip thin boards while giving good access from the right side to make feeding easier.
Or you can remove it, spin it 90 degrees clockwise and slot it back in to give you a bigger face with which to register thicker boards for ripping or wider boards for resawing. See that is has another T-track facing upwards in your photo.