What does 1200 cc in a car means?

the cc stands for cubic centimeters, so 1200 cc is the total displacement of the engine.

It is the total volume, that the cylinders would displace for each stroke.

For example. Suppose you have 4 cylinders in an engine. If each cylinder displaces 300cc for each stroke ( from Top dead centre to bottom dead centre), then it equals 1200cc for 4 cylinders.