Trataka is Sanskrit for concentrated gazing. I came across this term in The Hatha Yoga Pradipika , a classic 15th century yoga manual.
It is through concentrated gazing that we activate the inner mind. It is not concentration with tension but a steady gaze, a relaxed mind and body. I have used a candle for this and an art work that I created based on imagery that has come to mind during deep meditation. The candle flame and the central dot within the triangle are aligned so that I focus on the base of the flame and the dot behind it.
The practice is concentration with eyes open and a steady gaze, followed by eyes closed. When the eyes are closed the impression remains and one focuses on the impression behind closed lids. In the beginning the image is there and then wonders off, the mind becomes active with thoughts. Over time the image remains steady and we are in a calm composed state.