Which type of substance is described as compressible with no specific volume?

The nature of gases is defined by their compressibility and the absence of a definite volume. Unlike liquids and solids, gases do not have a fixed shape or volume and can expand to fill any container. This ability to compress means that gases can occupy varying amounts of space under different pressures and temperatures. When external pressure is applied, the volume of a gas decreases, demonstrating its compressible nature.

Liquids, on the other hand, have a defined volume but can change shape to fit the contours of their container. Solids maintain both a specific shape and volume, giving them rigidity. Aerosols are partly composed of liquid droplets or solid particles suspended in a gas, and while they exhibit some characteristics of gases, they do not fit the criteria of being entirely compressible or lacking a specific volume. Thus, gases are the only substances that can be described as compressible with no specific volume.