Question about "아가씨”

Could you explain to me when 아가씨 is used? 

<My Answer>

In korea these days "아가씨" is rarely used because it has a little bit weird meanings even though it has very much good meaning in the old days before the 1970s.

The reason is why ever since the 1980s used the word "아가씨" for a young woman who entertains male guests at a coffee shop(called as "다방”) or bar(called as "술집”, "선술집”), the word has gradually become obsolete as it begins to have a bad meaning.

Traditional usages has 3 cases

1) When a servant calls an unmarried woman of a master's house by honor during the Joseon Dynasty.

2) When the elder person calls young woman below approxmately the age of 30s.

3) When a man's younger sister calls a woman who married her elder brother.