What is Mapainik?

Legal Definition
Mapainik is a colloquial term for a member or supporter of Mapai, the historical Israeli Labour Party. The party has since changed its name to Ha'Avoda, but one can occasionally still encounter the term as an informal description for "old school" former and present members of Labour in Israel, especially those who defend a secular form of Zionism against more religious interpretations of the same ideology.
-- Wikipedia