So why do we have two names for them – are they Valves, or Vacuum Tubes?

Depends whether you’re using American or English terminology. UK tends to call them valves, Americans use Vacuum Tubes.

In the decades that have elapsed since they were the default technology, the distinction has become a little blurred. So these days the two are pretty much interchangeable. Older electronics engineers might show a preference for whichever term suits their culture, however.