What is Sva-dharma in the Bhagavad Gita?
Sva-dharma is your own dharma: the work that follows from what you actually are. 18.47 is the line everybody quotes. Better your own work done imperfectly than somebody else's done well.
Read as a line about vocation it is one of the most freeing sentences in the book. The imitation of someone else's excellent life is worth less than your own clumsy one, which stands against envy, against copying, and against the exhausting business of running a life you chose because it looked right.
Read as a line about social position it becomes an instruction to stay put, and that reading has a long and damaging history. Combined with a hereditary reading of the four varṇas, it told people born into service that service was their fault-free path and that reaching for anything else was the dangerous option. A reader deserves to know both readings exist. The verse itself supplies the test that separates them: it says the work follows from your nature. Work assigned by your parentage is not that, and any reading that cannot tell the difference between what you are and where you were born has lost what the sentence is about.
The verses 8
2.31
And if you look at your own work in the world, you have no reason to waver.
2.33
But if you will not fight this rightful fight, then you throw away your own work and your good name, and you take on the fault instead.
3.35
Better your own work, done badly, than someone else's work done well.
18.41
The work of the priestly, the ruling, the producing and the serving groups is divided, Arjuna, according to the qualities that arise from what each person actually is.
18.45
A person reaches fulfilment by taking delight in the work that is his own.
18.46
The one everything living comes out of, by whom all this is spread through: a person reaches fulfilment by honouring him through his own work.
18.47
Better your own work done imperfectly than someone else's work done well.
18.48
The work you were born to should not be given up even though it has faults in it, Arjuna.