तं विद्याद् दुःखसंयोगवियोगं योगसंज्ञितम्।स निश्चयेन योक्तव्यो योगोऽनिर्विण्णचेतसा॥
taṃ vidyād duḥkha-sanyoga-viyogaṃ yogasaṅjñitamsa niścayena yoktavyo yogo ’nirviṇṇa-cetasā
Word by word
The verse says
Know that the undoing of the connection with suffering is what is called yoga. That practice is to be practised with resolve, and with a mind that does not turn back.
In plain words
The sentence lands, and it is the Gita's own definition of the word.
Duḥkha-saṁyoga-viyogam — the disconnecting of the connection with suffering.
Not the removal of suffering. The removal of the joint.
Where you've felt this · at work
You come back to the same difficult report every morning for three weeks without once deciding whether you feel like it. That is the whole trick. There is no morning on which you feel like it.
Going deeper
The definition is built out of two opposite words and that construction is the whole meaning.
Saṁyoga is joining. Viyoga is unjoining. Yoga — which also means joining — is here defined as the unjoining of a joining. The word is being turned against itself on purpose.
And notice what is not promised. Suffering is not removed from the world or from your life. What is undone is the connection, the place where it fastens to you.
Then the instruction, which is the least mystical sentence in the chapter: practise it with resolve, with a mind that does not turn back. Anirviṇṇa-cetasā — with a mind that has not become disheartened.
That word assumes discouragement. It is not addressed to someone for whom this is going well. It is addressed to the version of you that has already tried and stopped, which is the version most people are by the time they reach this verse.