the subject of concentration has been brought up recently on a couple threads
i'll offer up a definition that occured to me.... 'the crystallisation of intent into detailed mental imagery'
& that keeping it might be to do with 'the clarity of intense familiarity' - hey if you can get it to rhyme that has to be a bonus - no ?
this might be complete bollocks, but there you go
Mental imagery is not concentration but it can be the subject of concentratIon.
Concentration is the capacity to bring the mind onto something and to bring back the mind back to that focus when It wanders. It is an exclusionary action which filters awareness exclusively on the object of focus.