Unfortunately, not working now :(

돌잔치 = 1st birthday celebration/party

영아사망률(infant mortality)가 과거에는 높았기 때문에 아이가 1년 이상 생존하면 옛날 사람들은 큰 의미를 부여헀던 것 같아요

Because infant mortality was very high in the old days, people in the past used to give some special meaning to the child's first birthday. The same logic applies to 백일 (100 days celebration)

잔치는 파티 (party)라는 뜻이에요. It means party.