What is the expansion and compression process?

Hint:To study the expansion or compression process, we analyze the change in volume of the matter.
The expansion process volume is a gradual increase in the volume of the matter.
The compression process volume is a gradual decrease in the volume of the matter.

Step-by-step solution:
Volume of a matter is defined as the space occupied by the matter. The SI unit of volume is cubic meter$\left( {{m}^{3}} \right)$.
1 cube meter is defined as the space occupied by a cube of each side of measurement of$1m$.
When space occupied by the matter gradually increases then the process is called expansion. And when the space occupied by the matter is decreased gradually then the process is called the compression pressure.
The volume of the gas is the volume of the container in which gas is confined in. The characteristics of gas are defined using physical quantities like pressure, volume and temperature.
Using ideal gas equation,
$PV=nRT$
Here,
$P=$The pressure of the gas
$V=$The volume of the gas
$n=$The amount of gas in moles
$R=$The universal gas constant
$T=$The temperature of the gas
Then the volume of the gas can be determined as,
$V=\dfrac{nRT}{P}$
If the container is not rigid, then change in other physical quantities will change the volume of the gas.

When pressure of the gas is kept constant and temperature of the gas is increased then volume of the gas increases. This process is called the expansion process. When the temperature of the gas is decreased then the volume of the gas also decreases, so it is a compression process.

When temperature of the gas is kept constant and pressure of the gas is increased then volume of the gas decreases. This process is called the compression process. And when the pressure of the gas is decreased then the volume of the gas increases, so it is an expansion process.

Note:
-The rigidity of the container of the gas must be kept in thought when analyzing the expansion and compression process. If the container is rigid then there will be no expansion or compression process.
-The system of the gas should be isolated from the surrounding. If the system is not isolated then the heat given to the system can escape from the system to the surrounding.