What is Yoga in the Bhagavad Gita?
Yoga comes from a root meaning to yoke or join, the same root as the English word yoke. In the Gita it almost never means physical postures. It means being joined to what is real, and the method by which a person gets there.
The book names several, and treats them as routes rather than rivals. Karma yoga is work done without the grip on its result. Jñāna yoga is the path of understanding. Bhakti yoga is the path of love. Dhyāna yoga is the meditation chapter 6 describes in practical detail, down to the seat and the posture and the gaze.
Two definitions inside the text are worth keeping. 2.48 says yoga is evenness of mind, the same in success and failure. 2.50 says yoga is skill in action, which is a strange and useful thing to call a spiritual state. Put together they describe something closer to a way of working than a way of withdrawing, which is why the Gita keeps insisting that the household and the battlefield are not worse places to practise than a cave.
The verses 17
2.48
Stand in yoga and do your work, Arjuna, letting go of the holding-on.
2.50
A person joined to that mind sheds both the good he has done and the bad, right here in this life.
2.53
When the scriptures have stopped pulling you about, and your mind stands still and unmoved, then you will have yoga.
4.1
Krishna said: I taught this unfading practice to the sun.
4.2
Passed down like that, the kings who were also seers knew it.
4.3
That same ancient practice is what I have told you today.
5.4
Children say that analysis and practice are separate things.
5.5
The place reached by analysis is reached by practice too.
6.2
Know that what they call renunciation is the practice itself, Arjuna.
6.3
For a sage who wants to climb to the practice, work is called the means.
6.10
The practitioner should join himself constantly, staying in a solitary place, alone, with mind and self restrained, expecting nothing, holding nothing.
6.16
Practice is not for the one who eats too much, nor for the one who does not eat at all - nor for one given to too much sleep, nor for one who stays awake, Arjuna.
6.17
For the one whose eating and moving are measured, whose effort in his work is measured, whose sleeping and waking are measured - the practice becomes a killer of sorrow.
6.19
As a lamp standing where there is no wind does not flicker - that is the likeness remembered for the practitioner of restrained mind, joining himself to the practice of the self.
6.23
Know that the undoing of the connection with suffering is what is called yoga.
6.46
The practitioner is greater than those who do austerities, and greater, it is held, than those who have knowledge, and greater than those who do works.
6.47
And of all practitioners, the one who has gone into me with his innermost self, full of trust, devoted to me - he is held by me to be the most joined of all.