Mixture
Definition
Two or more substances physically combined without chemical bonding. Air, salt water, and trail mix are mixtures you can separate by physical means.
Technical definition
A mixture is a physical combination of two or more substances in which each retains its chemical identity and the proportions can vary. Components are separable by physical methods such as filtration, distillation, or evaporation. Mixtures may be homogeneous (uniform) or heterogeneous (non-uniform).
Example
Salt dissolved in water is a homogeneous mixture. Sand mixed with iron filings is a heterogeneous mixture that can be separated with a magnet.
Common confusion
Dissolving is not a chemical reaction: salt water is still a mixture, because the sodium and chloride ions are not chemically bonded to the water.