A formal written notice submitted when resigning from a position, especially in a company or organization.
He submitted his letter of resignation to the president.
You should think carefully before writing your letter of resignation.
He submitted his resignation letter to the president.
She formally submitted her resignation letter effective next month.
His boss accepted his letter of resignation.
He thought it over and withdrew his letter of resignation.
辞表 is a formal, definitive letter of resignation submitted when someone is leaving a job for good, whereas 進退伺い is a tentative notice asking a superior to decide whether one should stay or step down, often after a mistake.
辞書 in its archaic second sense meant a letter of resignation, but modern Japanese uses 辞表 instead for that meaning.
Compound of 辞 (resign, word) and 表 (document, table), literally 'resignation document'.