The term "physical state" refers to the distinct forms that different phases of matter take on. The most common physical states are solid, liquid, and gas. Each state has unique properties, such as shape and volume. For example, solids have a fixed shape and volume, while liquids have a definite volume but take the shape of their container. Gases, on the other hand, have neither a fixed shape nor a fixed volume, expanding to fill the available space. The physical state of a substance can change due to variations in temperature and pressure. For instance, heating a solid can cause it to melt into a liquid, while further heating can turn the liquid into a gas. Conversely, cooling a gas can lead to condensation into a liquid, and further cooling can solidify it. These transitions are essential in various scientific and industrial processes.