Dhyāna (Sanskrit) or Jhāna (Pali) means meditation in Hinduism, Buddhism and Jainism. In Buddhism, it is a series of cultivated states of mind, which lead to “state of perfect equanimity and awareness (upekkhii-sati-piirisuddhl).”
According to Henepola Gunaratana the term “jhana” is closely connected with “samadhi”, which is generally rendered as “concentration.” The word “samadhi” is almost interchangeable with the word “samatha,” serenity.
In the suttas samadhi is defined as mental one-pointedness. Buddhaghosa explains samadhi etymologically as
… the centering of consciousness and consciousness concomitants evenly and rightly on a single object… the state in virtue of which consciousness and its concomitants remain evenly and rightly on a single object, undistracted and unscattered (Vism.84-85; PP.85).
In the widest sense the word samadhi is being used for the practices which lead to the development of serenity. In this sense, samadhi and jhana are close in meaning. Nevertheless, they are not exactly identical. Samadhi signifies only one mental factor, namely one-pointedness, while the word “jhana” encompasses the whole state of consciousness.
Samadhi also covers another type of concentration, namely “momentary concentration” (khanikasamadhi), “the mobile mental stabilization produced in the course of insight contemplation of the passing flow of phenomena.”