Beautiful answers from the heart!
The way I see it, words like concentration, meditation, contemplation, realization etc. are used by many to refer to many different states of mind. It can get very confusing if we do not remain undistracted by all these thoughts.
Personally I would describe concentration as it is mostly practiced as simply concentrating on one object and keeping out all other thoughts. But there are two ways concentration can unfold itself.
When coupled with belief in what one is doing, with intention to reach some state of mind, it is the concentration that leads to a cultivated state of mind. In other words: a state that you allows yourself to be blinded/absorbed by; a state that somewhat resembles the state of true openness and understanding as a quality, but is in fact merely a very well developed, a very refined, thought.
Basically what one does, in my observation, is that one chooses the kind of reality one wants by choosing that single thought-form to concentrate on until it becomes total and absorbs attention completely. When this happens, many call it meditation or even samadhi. But as yoga tells us too, samadhi, especially this kind of samadhi, is still maya :). Since all we are truly doing is pick one reality (thought actually) to lose ourselves in without remaining open to whatever is. While wisdom is open and inclusive of everything. It is, in my experience, not dependent on any sort of contrived state of mind.
Concentration.contemplation/meditation, in my vocabulary, can also mean an open quality of presence that’s simple aware of its own presence.
In this instance concentration is not coupled with ideas and concepts about right and wrong, spiritual and non-spiritual, distractions and attainment/goal. In this second way of concentration, one is simply not distracted by whatever appears, including concentration or non-concentrated states. This type of concentration is not cultivated through exerting and perpetuating a single belief/idea/thought and excluding all others until that one thought-quality becomes a state of mind. This second concentration is simply open mindfulness to whatever is, without trying to create a result in the mind, without rejecting or accepting any one thought or reality. This natural openness to whatever is, is attention being aware of its source in the Now. It is Compassion, natural understanding and it unleashes True Love.
Love,
Bentinho.