Matter that has no size or shape of its own is called a fluid.

Here's why:

* Fluids take the shape of their container: This is a key characteristic of fluids. Whether it's a liquid like water or a gas like air, they will mold to fit the container they are in.

* Fluids have no fixed shape: This is a direct result of their ability to flow and adapt. They can be poured, squeezed, or compressed, and their form will change accordingly.

While the term "fluid" is most commonly associated with liquids, it technically encompasses both liquids and gases.