water vapor

This term is used primarily in scientific, meteorological, and technical contexts to describe the gaseous phase of water. It is distinct from "steam," which often refers to water vapor that has become visible as a mist or is produced by boiling, whereas water vapor is inherently invisible to the human eye.

As a mass noun, it describes a substance rather than individual units. It is typically used with quantifiers like "amount of" or "concentration of" rather than numeric counts.