a young woman who has reached the age to marry and bear children
This is a word about a stage of life, not a sexual status. An עַלְמָה is a girl who has grown past childhood into the years when she can marry and have children:
- physically mature
- of an age to be courted
- typically still unmarried and living under her father's care
The related word for a young man, עֶלֶם, makes the point plain. When King Saul asks whose son the עֶלֶם is, he means a vigorous young fellow, not a chaste one. The feminine simply names the same season of life in a woman.
Because an unmarried young woman in ancient Israel was assumed to be a virgin, the word often does describe one. But that purity comes from the situation, not from the word itself. The same word covers Rebekah before her marriage, the girl Miriam watching over baby Moses, the young women drumming in a festival procession, and the courted woman in the love poetry of the Song. What ties them together is youth and readiness for marriage, not a claim about virginity.