"Static fire" = holding down the rocket and firing the engines for some time. It's a rehearsal of the whole launch procedure short of actually releasing the rocket.
The point of a static fire is to test the launch systems. The hope is that problems can be noticed before the actual launch, where they are more likely to cause catastrophic failure (and where we they might not be noticed in time to abort).
Better to have the rocket explode on the pad in a controlled test than in the air over a populated area.