What is the different between "USB2 BIAS PAD" and "USB2 PAD"?

Hello I am a newbie for TX1 and am just reading the X1 datasheet.
I am right now studying the X1 USB complex chapter and from USB description I see “Each Tegra X1 device provides
two USB 2.0 controllers with five USB interfaces: four regular USB ports and one HSIC” but from USB block diagram there is one additional “USB2 BIAS PAD”–which looks not be described in the document.
search in context I can not find much detail of the “USB2 BIAS PAD”.
So anyone can help to explain a little more about this additional USB port?

The USB Bias pad generates reference voltage and bias currents for USB2 IO pad macro. The IREF output of the bias pad is the reference bias current and it generates one branch per IO pad.

Hello I am still a little confused–that means it is a voltage ref. pads for all the USB PHY logic?
is that a supply input (for exp, 1.8V) from PMIC, or an internal logic pad that does not exposed?
as on TX1 SCHEMATIC I did not find the relevant pads–or maybe I am not enough patient;-)

Yes, it is internal and does not exposed.