numeric
The number three, used in counting, mathematics, and Sino-Japanese compounds. The reading サン is the on'yomi; the native Japanese reading み is not covered here.
from Chinese sān
三に二を足すと五になる。
Three plus two equals five.
このクラスには三つのグループがある。
There are three groups in this class.
The native Japanese counter for three items, used with the kun'yomi reading み. 三 (サン) is the Sino-Japanese number used in compounds and counting.
From Middle Chinese 三 (sam). The reading サン is the regular Sino-Japanese on'yomi.