Decorations are finishes and textures applied to the movement of a watch, originally to mask tool marks and trap dust. Nowadays, they're mostly used as eye candy and to denote more expensive movements.
You can see perlage, blued screws and a bit of Cote du Geneve on the rotor. For contrast, here's a base-grade ETA 2824:
Basic colimaconnage on the rotor; not much else.