These are concentrated states, rather than the act of concentrating, which pertains more to right effort.
They are states in which the mind’s energies have been unified, in the form of the four jhanas, lucid meditative trances.
Source: Excerpted and adapted from Peter Harvey, An Introduction to Buddhism: Teachings, History and Practices, 2nd ed, (Cambridge: Cambridge University Press, 2013), page 83.
Right Concentration is the means for training and centering the mind. Through Right Concentration we bring our ordinarily restless, unconcentrated mind into a state of tranquility, one-pointedness, and unbroken attentiveness. By training the mind through Right Concentration, we extinguish the delusion, self-centered desire, and destructive thinking that rule the scattered, untrained mind. In this way, we develop serenity and mental/emotional stability, and we gain insight into the true nature of reality.
Right Concentration leads one through the various stages of Dhyana (meditation) into equanimity, joy, purity of mind, and attainment of the highest wisdom. Right Concentration is a fully engaged means of training the mind and heart to be completely present in each moment, without cutting ourselves off from others or escaping the responsibilities of life. Through Right Concentration we cultivate mental discipline/concentration (samadhi), an essential aspect of the Path.
Source: SourcePoint Global Outreach, The Heart of Dharma Collection (Mount Shasta, CA: Naljor Prison Dharma Service, n.d.) http://sourcepointglobaloutreach.org/what-we-offer/