It routes the signal through a Low Cut or High Pass Filter (same thing) which reduces the amplitude of the low frequency portion of the signal. That filter has a specific slope (common is -6, -12, -18, -24, -48dB/octave, I'd guess it's -12 or -24dB/octave in this case) which describes the degree of attenuation below a specific corner frequency, which is the frequency where the signal measures -3dB down along the slope. I don't know what that specific slope and corner frequency is, but it should be specified in the manual.
..just checked the manual online and the corner frequency is selectable in the Input Setup menu, under Low Cut Freq. Options are 100Hz, 200Hz, or 400Hz. It does not specify what the slope is.