This kind of steel bar with lines on it is collectively called "deformed steel bar", also known as "ribbed steel bar", which corresponds to "light round steel bar" without lines. This kind of pattern is called "transverse rib", and the common shapes of transverse ribs are spiral, herringbone and crescent.
The transverse ribs on the steel bar are used to enhance the bonding performance between the steel bar and the concrete, and to better transfer stress. Simply put, it is to make the steel bar and the concrete work better in coordination and jointly bear external forces.
The cross-sectional view of the cross-rib bar with crescent pattern on both sides, you can see why it is called "crescent shape":
