A somewhat dated or literary term for an eraser; 消しゴム is far more common in modern everyday speech.
See also: 消しゴム
In the old days, we used to erase pencil marks with a 字消し.
Compound of 字 (character) and 消し (erasing), literally 'character eraser'. The exact historical origin is uncertain, but it likely predates the widespread use of rubber erasers.