i just browse through the meaning of right concentration in some website...
Right concentration is one of the eight element in the Noble eightfold path.
Right concentration (samyak-samadhi · samma-samadhi), together with right mindfulness, is concerned broadly with the practice of Buddhist meditation.
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And what, monks, is right concentration?
(i) Quite withdrawn from sensuality, withdrawn from unwholesome states, a monk enters in the first jhana: rapture and pleasure born from detachment, accompanied by movement of the mind onto the object and retention of the mind on the object.
(ii) With the stilling of directed thought and evaluation, (he/she) enters and remains in the second jhana;na: rapture and pleasure born of concentration; fixed single-pointed awareness free from movement of the mind onto the object and retention of the mind on the object; assurance.
(iii) With the fading of rapture, (he/she) remains in equanimity, mindful and fully aware, and physically sensitive of pleasure. (He/She) enters and remains in the third jhana which the Noble Ones declare to be "Equanimous and mindful, (he/she) has a pleasurable abiding."
(iv) With the abandoning of pleasure and pain...as with the earlier disappearance of elation and distress...(he/she) enters and remains in the fourth jhana;na: purity of equanimity and mindfulness, neither in pleasure nor in pain.
This, monks, is called right concentration[17].
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1) And what does it mean by movement of mind onto object?
Vitakka (Pali) or Vitarka (Sanskrit), both in Hinduist yoga and Buddhist meditation, means the action of taking care of any object : God, one's body, the Self, a color, any sensation, any things...
It refers to attention in a different way than cognitive neuroscience, implying a very strong leading of attention, as it leads to more mental process : Vicara piti, sukha and ekaggata.
Vitakka is the first element to appear in meditation's process, still present in the first Jhana, but absent of any further Jhana.
2 )And what does it mean by retention of the mind on the object:
Vicara is a term of buddhist psychology. This term is mostly used to describe the internal feeling of the yogi who practices samatha bhavana, that is the meditation technique consisting in focusing the mind to one single point. Nevertheless, this term can be used to describe the practice of vipassana or even, outside of any meditation context, the simple fact to maintain awareness on any object.
In the meditation practices, the mind catches a mental object (see: vitakka), which means the meditator try to notice a feeling and to stay aware of it. He cultivates consciousness of this object - and the term object is understood as a psychological object, a perception.
Vicara is focusing on an object, and holding it in consciousness, to meditate on it - Like meditating over a candle flame. You meditate on the flame, watch it move, so eventually you are no longer yourself, but you can "become" the flame. The meditator focusses all his attention on the object but not on the self image, or the distinction between himself and his environment.
Vicara eventually become one of the five factors of the first jhana.