An ostracon (Greek: ὄστρακον ostrakon, plural ὄστρακα ostraka) is a piece of pottery, usually broken off from a vase or other earthenware vessel. In an archaeological or epigraphical context, ostraca refer to sherds or even small pieces of stone that have writing scratched into them. Usually these are considered to have been broken off before the writing was added; ancient people used the cheap, plentiful and durable broken pieces of pottery around them as a convenient medium to write on for a wide variety of purposes, mostly very short inscriptions, but in some cases very long.
In Classical Athens, when the decision at hand was to banish or exile a certain member of society, citizen peers would cast their vote by writing the name of the person on the shard of pottery; the vote was counted and, if unfavorable, the person was exiled for a period of ten years from the city, thus giving rise to the term ostracism. Broken pottery shards were also used for anal hygiene. Scholars have suggested that shards from a vote may have been re-used for this purpose, to curse the exiled individual by soiling their name.
Anything with a smooth surface could be used as a writing surface. Generally discarded material, ostraca were cheap, readily available and therefore frequently used for writings of an ephemeral nature such as messages, prescriptions, receipts, students' exercises and notes. Pottery sherds, limestone flakes, and thin fragments of other stone types were used, but limestone sherds, being flaky and of a lighter colour, were most common. Ostraca were typically small, covered with just a few words or a small picture drawn in ink; but the tomb of the craftsman Sennedjem at Deir el Medina contained an enormous ostracon inscribed with the Story of Sinuhe.
The importance of ostraca for Egyptology is immense. The combination of their physical nature and the Egyptian climate have preserved texts, from the medical to the mundane, which in other cultures were lost. These can often serve as better witnesses of everyday life than literary treatises preserved in libraries.