Liquids are known as fluids because they share a key characteristic with gases: they can flow.

Here's why:

* Fluidity: Both liquids and gases lack a fixed shape and can easily change their form under the influence of external forces. This ability to flow is the defining characteristic of a fluid. Imagine pouring water or air into a container – they take the shape of the container.

* Molecular Structure: The molecules in liquids and gases are not rigidly bound together like those in solids. This allows the molecules to move past each other freely, leading to their fluidity.

While liquids and gases share this ability to flow, they differ in other ways. For example, liquids are much denser than gases and have a more defined volume, while gases expand to fill their containers.

So, the term "fluid" encompasses both liquids and gases, emphasizing their common property of being able to flow.