Unsaturated Definition in Chemistry

The Two Meanings of Unsaturated

This is the chemical structure of propyne, an unsaturated compound.
This is the chemical structure of propyne, an unsaturated compound. Todd Helmenstine

In chemistry, the term "unsaturated" can refer to one of two things.

When referring to chemical solutions, an unsaturated solution is able to dissolve more solute. In other words, the solution is not saturated. An unsaturated solution is more dilute than a saturated solution.

When referring to organic compounds, unsaturated means a molecule contains double or triple carbon-carbon bonds. Examples of unsaturated organic molecules include HC=CH and H2C=O.

In this context, being saturated can be thought of as being "saturated with hydrogen atoms."