After a normal inspiration and expiration, an adult patient has about 2,400 ml of air remaining in the lungs, known as the:

Functional residual capacity (FRC)is the volume of air that will remain in lungs after normal expiration.
Check for more information:
(https://en.m.wikipedia.org/wiki/Functional_residual_capacity
Functional residual capacity - Wikipedia)

It is known as the functional capacity. 

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