Holding the body, head and neck straight and unmoving, staying steady, looking at the tip of his own nose and not glancing in any direction…
Explanation
Krishna is continuing his instructions to Arjuna on how to sit for meditation (dhyāna-yoga, the discipline of steadying the mind). Here he describes the posture: the back, head and neck in a straight line, still, with the gaze fixed and not wandering. Some traditions take "the tip of the nose" literally, while others read it as a half-closed gaze directed roughly that way, or as a focus between the eyebrows. The sentence carries on into the next verse.