Labeling terminals and junctions in a BJT
what does the line with an empty circle (the terminal symbol) really
  represent? My understanding is, it is simply used to represent the
  label the voltage at junction/node. Is this correct?    


They are just tapping points or nodes. I think them like an option to connect or insert a wire. it can be input (\$V_B\$) or output (\$V_C\$). It is just a representation to tell that one can either connect an input or a load or even simply a measuring device (DMM for example).