Partial pressure is the pressure exerted by an individual gas within a mixture. So think of it as the gas's individual pressure. We're going to say in a container of unreacting gases, the total pressure of the container is the sum of partial pressures of each gas.
Now this is known as the law of partial pressures. So basically, the total pressure inside of a container comes from adding up all the pressures of each individual gas. Total pressure would equal the pressure of gas one plus gas two plus gas three and so on if there are additional gases.
So just remember, the total pressure that a container is experiencing is contributed by each of the individual gases within it.
