That is partly because it carries both agricultural and revelatory meanings.
Shavuot came to mark the giving of the Torah
Britannica explains that Shavuot is the Jewish holiday associated in rabbinic Judaism with Moses' reception of the Torah at Mount Sinai.
That theological meaning is now the one most Jews know first.
It began as a harvest festival
Britannica also notes that Shavuot originally marked the wheat harvest and the offering of first fruits in Temple times.
This double structure matters. Shavuot ties land and revelation together, showing how agricultural life and covenantal memory became layered in Jewish tradition.
The holiday follows the counting of the Omer
Britannica explains that Shavuot comes after seven weeks of counting from Passover. That rhythm gives the holiday a different feel than fixed-date festivals like Rosh Hashanah.
It arrives as a culmination.
Why it still matters
Shavuot still matters because it links freedom to law. Passover alone tells the story of release. Shavuot asks what that freedom is for.
The shortest accurate answer
Shavuot is the Jewish festival associated with the giving of the Torah at Sinai and, in its older biblical layer, with the agricultural harvest and first fruits.