To ostracize is to cast someone out, or expel them from the community. In Ancient Greek, it means to banish because of a vote.
Etymology
The etymology of ostracize is fascinating: It comes directly from the Greek verb ostrakízein, which is itself akin to ostrakon, the shell of an oyster—during votes to ostracize a member of a community, votes were inscribed on oyster shells to be counted after the vote was done.