What was the Saturn V rocket's third stage called?

What was the Saturn V rocket’s third stage called? It was called the S-IVB.

The Saturn V had three propulsion stages: the S-IC first stage, the S-II second stage, and the S-IVB third stage. The S-IVB was built by Douglas Aircraft Company and used a single J-2 engine fueled by liquid hydrogen and liquid oxygen.

For Apollo lunar missions, the stage performed two crucial burns. Its first burn helped place the spacecraft into Earth orbit; after the astronauts and ground controllers checked the systems, a second restart sent the Apollo spacecraft toward the Moon in translunar injection.

The name can be confusing because the S-IVB also served as the second stage of the smaller Saturn IB. The “S” indicated a rocket stage, while “IVB” reflected its development from the earlier S-IV stage. After Apollo 13, spent S-IVB stages were often directed to impact the Moon, producing seismic signals for lunar science.