The state of matter described in your question is known as a gas.
In a gas, the particles are much farther apart compared to solids and liquids. This spacing allows them to move freely and embrace a random, irregular arrangement. Because of this freedom of movement, gas particles fill the shape of their container and can expand to occupy a larger volume if given the space.
The collisions between gas particles and with the walls of their container lead to pressure, which is a fundamental property of gases. Unlike particles in solids, which are tightly packed in a fixed arrangement, gas particles can move rapidly in all directions, leading to their characteristic behaviors, such as diffusion and the ability to compress.