करुणा

Karuna means compassion: the feeling that wakes when another is in trouble and moves one to act for their good. In chapter 12 it stands beside friendliness among the marks of the devotee (Gita 12.13). The verse has the word in the form "karuna".

The ground of it is seen in chapter 6. The one who sees the pleasure and pain of others as his own is called the best yogi (Gita 6.32). That is where compassion comes from: another's trouble felt as one's own. Its fruit is being intent on the good of all beings (Gita 5.25, Gita 12.4).

Compassion and grief are different. Grief sinks a person and stops the hand; the Lord told Arjuna not to grieve for those who are not to be grieved for (Gita 2.11). Compassion feels another's trouble and does not itself waver, which is why it can act.

Common misreading: that compassion means sinking into another's sorrow and becoming sad oneself.

Better sense: taking another's trouble as one's own and, staying steady, going to work for their good.

The whole passage is in The Devotee Dear to the Lord.