। ॥ ३७८ ॥
In plain words
The air that takes the juices of the food you have eaten and spreads them evenly through the whole body — equalizing is simply what it does, and that is where its name comes from — is what is meant by samāna, the fifth of them.
Close to the Sanskrit
Because of its property of equalizing the juices and the rest of the food that has been eaten, that air which is the fifth among them is meant by the term 'samāna'.