prefix
the three great ...; the big three ...
Prefix used to refer to the three most prominent or representative things in a category, often in fixed compounds like 三大疾病 (the three major diseases) or 三大都市 (the three major cities).
See also: 三大疾病
日本三大祭りは、京都の祇園祭、大阪の天神祭、東京の神田祭です。
The three great festivals of Japan are Kyoto's Gion Festival, Osaka's Tenjin Festival, and Tokyo's Kanda Festival.
世界三大珍味といえば、キャビア、トリュフ、フォアグラです。
Speaking of the world's three great delicacies, they are caviar, truffles, and foie gras.
Compound of 三 (three) and 大 (big, great). The prefix usage is a straightforward Sino-Japanese formation.