What does "voltage2" mean in ad9361 evaluation linux system?

I am trying to debug a  self-build board based on FMCOMMS2. When I run ad9361 linux system on it, in DDM page of the AD9361 oscilloscope  window, there is one parameter called "ad9361:phy voltage2", what does it mean? Which voltage does it mean in ad9361 board? I appreciate any useful information.