(Greek: ὄστρακον). Plural: ostraka. A broken piece of a pottery vessel used as a writing surface. The inscription can be written in ink or scratched into the surface of the pottery.  In ancient Athens citizens would cast their votes to exile another citizen by scratching his name on a shard of pottery (this is the origin of the word “ostracize”). Web resource here.

Ostraka inscribed with the names Aristides, Themistokles, Kimon and Perikles. Fifth century BCE. Agora Museum, Athens.