A stillbirth is when a baby is born dead after having grown far enough that the birth is a birth — not a very early loss. Most countries draw a line by week or by weight (often around 20 to 24 weeks) and call a loss before that line a miscarriage, and after it a stillbirth. So the two words are not about how sad the event is; they are about when it happened.

This is a plain, factual word, and that plainness is why it exists. Doctors need it, forms need it, the law needs it, and grieving parents themselves often want it, because the alternatives are either vague ("we lost the baby") or unbearable. So it is used freely in hospitals, in health writing, and in support groups, without being cold.

The related forms are worth having together: a baby who is born dead is stillborn (adjective), and the event is a stillbirth (noun). "She had a stillbirth" and "the baby was stillborn" say the same thing.

There is a figurative use of stillborn — a plan or a proposal that dies before it can begin: "the peace talks were stillborn." That use is fine in writing about politics. But stillbirth itself stays literal; people almost never stretch it that way.

One thing to know before you speak: this word touches a real grief, and in English-speaking countries it is not a topic raised lightly with someone you do not know well.