In which state of matter are atoms free to slide over and upon each other?

In a liquid, atoms have enough energy to move past one another, allowing them to slide over and against each other. This property is what gives liquids a definite volume but no fixed shape; they take the shape of the container they are in. The atoms in a liquid are still closely packed, but the intermolecular forces are not strong enough to keep them in a fixed position, leading to fluidity.

In contrast, solids have tightly packed atoms that vibrate in place but do not have the freedom to slide. Gases consist of atoms that are much further apart and move freely in all directions, but they do not have the capacity to slide past each other as a cohesive unit like a liquid does. The term "semi-solid" is not a standard state of matter and can refer to materials that exhibit properties of both solids and liquids, but they do not fit the conventional definition of a state where atoms can slide over each other. This highlights the unique properties of liquids relative to other states of matter.