The dhyanas in Buddhism.

There are two main types of Buddhist meditation:

1. Concentration or tranquil meditation (samatha-bhavana)
2. Insight meditation (vipassana-bhavana)

As the concentration of the mind becomes deeper and deeper, different stages of calmness and joy called Jhana or deep mental absorptions arise which are free from any mental hindrances. The deep state of concentration and the removal of mental hindrances can be the necessary foundation for the development of insight or wisdom into the real nature of physical and mental phenomena.

When well developed, each of the five Jhana factors can suppress one of the five mental hindrances as follows;

• Initial application (vitakka) suppresses sloth and torpor (thina middha)
• Sustained application (vicara) suppresses sceptical doubt (vicikiccha)
• Rapture (piti) suppresses ill-will (vyapada)
• Mental bliss (sukha) suppresses restlessness and remorse (uddaccha-kukkuccha)
• One-pointedness (ekaggata) suppresses sensual desire (kamacchanda)

Insight meditation helps the meditator to gain an insight into the three common characteristics of all aspects of mentality and materiality (nama-rupa) namely; impermanence (anicca), suffering (dukkha), and not-self (anatta).

Jhana has been referred to in the English language as deep mental absorptions.

In the Theravada teachings, there are four fine material states (rupa jhana) and four immaterial states (arupa jhana) which can be attained through concentration meditation.

The four fine material Jhanas (rupa jhana)

1. First Jhana
2. Second Jhana
3. Third Jhana
4. Fourth Jhana

The four immaterial Jhanas (arupa jhana)

1. The sphere of boundless space ( akasanancayatana)
2. The sphere of boundless consciousness (vinnanancayatana)
3. The sphere of nothingness (akincannayatana)
4. The sphere of neither perception nor non perception  (nevasannanasannayatana)

The first Jhana

When concentration is established associated with the first two Jhana factors of initial application (vitakka) and sustained application of attention (vicara) on the counterpart sign of the meditation subject, the third Jhana factor of rapture (piti) arises followed by the fourth Jhana factor of happiness (sukha). The fifth Jhana factor of one-pointedness of the mind (ekaggata) keeps the mind still and rested, so the first Jhana is associated with all the five Jhana factors. In the first Jhana, the five Jhana factors must be able to completely suppress the five hindrances and involve the mind in the meditation object with the intensity of absorption. 

The second Jhana

Then by further developing the remaining three Jhanic factors of rapture (piti), happiness (sukha) and one-pointedness of the mind (ekaggata), the meditator enters the second Jhana.

The third Jhana

Then by abandoning rapture and further developing the two Jhana factors of happiness (sukha) and one-pointedness of the mind (ekaggata), the meditator directs his effort to enter the third Jhana.

The fourth Jhana

When the meditator intends to consider entry into the fourth Jhana based on the counterpart sign as the object, he has to consider the imperfect nature of happiness (sukha) in the third Jhana which is now felt as a gross sensation. By abandoning it and developing one-pointedness (ekaggata) further along with equanimity (upekkha) of the mind he enters the fourth Jhana. Equanimity has been present in the three previous Jhanas as well but, it has now developed to the full. The equanimity here is referred to as the feeling of neither pleasure nor pain. In the fourth Jhana, there is also well-developed mindfulness purified by equanimity.

The four immaterial Jhanas (arupa jhana)

The sphere of boundless space (akasanancayatana)

The meditator now extends the limit of the initial meditation object infinitely and then having come out of the fourth Jhana, continue to contemplate on the emptiness of the infinite space as the object of meditation reflecting on it as “boundless space” or just “space, space,” to attain the sphere of boundless space.

The sphere of boundless consciousness (vinnanancayatana)

With further increase in concentration and by entering and emerging from the sphere of boundless space, the meditator now shifts the attention from infinite space to infinite consciousness reflecting it as “boundless consciousness” or simply as “consciousness”. 

The sphere of nothingness (akincannayatana)

The meditator now focuses on the absence or non-existence of consciousness in the sphere of boundless space as the object of meditation by reflecting it as “there is not” or “void, void”. Then the meditator will enter the sphere of nothingness where the two Jhana factors of one-pointedness and equanimity are still present.

The sphere of neither perception nor non-perception (nevasannanasannayatana)

The meditator shifts the focus from the sphere of nothingness to the four aggregates of feeling, perception, mental formation, and consciousness contemplating them as “peaceful” which will eventually lead to the sphere of neither perception nor non-perception. This Jhana is the highest state of concentration of the mind that a meditator can attain in which the mental functions consist of only very subtle perceptions with no gross perceptions.

NB:

The five hindrances to mindfulness are: 

• Sensual desire: The mind is drawn to the sense world, with sounds, colors, and ideas that may be interesting. 
  
• Ill will: Can make a person irritable, bad-tempered, and suspicious. 
  
• Sloth and torpor: A dullness of the mind, where a person may not want to devote time and effort to process new information. 
  
• Restlessness and worry: A feeling of being distracted, irritable, or in constant motion.  
• Doubt: Can overwhelm the mind and prevent it from working to understand itself. 
  

Excerpts from: https://drarisworld.wordpress.com/2020/07/12/jhanas-in-theravada-buddhist-meditation/