[Wobbles42]

"Steam" is very definitely the gas phase of water. Water vapor is too. If we are talking about chemistry they are essentially synonyms.

If we are talking engineering, the term steam generally implies water vapor that is at or above the saturation temperature.

In every day usage they are usually drawing a distinction between visible and invisible water vapor, usually caused by the presence of liquid droplets, with "steam" being essentially "fog", but hotter.