Traditional Yoga, as set out by patanjali in his Yoga sutras, consists of eight ‘paths’. The first five are called bahiranga sadhana (external aids to Yoga), and the last three are called antaranga sadhana (internal aids to Yoga).
Dharana is the sixth limb of Yoga and the first step in meditation – deep concentration and focus. In Dharana the meditator is aware of their action in meditating and aware that they are seperate from the object of meditation.
Many people develop their skills in dharana by meditating on a physical object such as an attractive image, an image of a deity or a candle flame. Having gazed upon the external object they then try to hold the image in their mind.