Machatzit HaShekel

At the time when the Temple was standing, the Israelites would donate a half shekel and send it to the Temple for the purpose of purchasing communal sacrifices.

The source from the Torah appears in the portion of Ki Tisa: ki tisa et rosh b'nei yisrael lifkudeihem v'natnu ish kofer nafsho la'Hashem b'fokod otam v'lo yihiyeh bahem negef b'fokod otam: zeh yitnu kol ha'over al hapkudim machatzit hashekel b'shekel hakodesh esrim gerah hashekel machatzit hashekel terumah la'Hashem: kol ha'over al hapkudim miben esrim shanah vama'lah yiten terumat Hashem: he'ashir lo yarbeh v'hadal lo yam'it mimmachatzit hashekel latet et terumat Hashem l'khaper al nafshoteichem

According to the Sephardic custom
As per the amount they used to give when the Temple was standing, which is about nine grams of pure silver.

According to the Ashkenazi custom

In accordance with the ruling of the Rema who wishes to make a "remembrance for the half shekel in completeness shall give three coins that are marked with a value of half.