What does the line to line voltage mean?
In a wye or star connected system there are 4 wires available as shown below: .
Source:
The phase voltage is the voltage between any of the phases ABC and the neutral. Therefore Van is the phase voltage and Vna is the same thing, just reversed. The line to line voltage is the voltage between any two of the three phase wires ABC, e.g. Vab.
With delta, there is no neutral wire available and so the voltage between any two of the three available phase wires is the line voltage by default.