The water is converted into steam and the steam is concentrated at a point. The railway engine moves. All these are instances of concentrated waves. Even so, if you collect the dissipated rays of the mind and focus them at a point, you will have wonderful concentration. Real Raja Yoga starts from concentration.
Concentration merges in meditation.
Concentration is a portion of meditation. Meditation follows concentration. Jivanmukti leads to emancipation from the wheel of birth and death. Therefore, concentration is the first and foremost thing a Sadhaka or aspirant should acquire in the spiritual path. You are born to concentrate the mind on God after collecting the mental rays that are dissipated on various objects.