The form of matter without a definite shape or volume is gas.

Here's why:

* Shape: Gases take the shape of their container. If you put a gas in a bottle, it will fill the entire bottle. If you put it in a balloon, it will take the shape of the balloon.

* Volume: Gases expand to fill the available space. Unlike solids and liquids, which have a fixed volume, the volume of a gas changes depending on its container.

Let me know if you'd like to know more about the states of matter!