there are two types of vehicles called armored car: one is a light truck, modified with armored plates, bulletproof glass, gun ports and other security measures. It is used to transport precious stuff, like money and stamps.
The other, and possibly more interesting, is a war vehicle born before the tank, consisting basically of an armored and beweaponed light truck able to move offroad.
The first war armored car was the Ehrhardt Panzerautomobil zur Verfolgung von Luftballons (armored car for the pursuit of balloons). Built around a truck chassis and protectected by 3 mm steel plates (quite thin, probably good only for stopping shrapnel) and armed only with a Rheinmetall 50 mm cannon, this was definitely a specialized weapon.
Subsequent developments saw the armored car fitted with machine guns, and used in recon roles during both wars.
The armored car shone particularly in the desert war (read about it in Lawrence of Arabia's Seven Pillars of Wisdom), where its speed and agility allowed it support infantry well.
The armored car spawned the APC, and it should not be confused with the light tank; an armored car always has wheels, a tank has treads.