尺牍 (chǐ dú) literally means 'one-chi-long wooden tablet' — a traditional Chinese writing surface made of bamboo or wood, approximately 23 centimeters long (the length of one ancient chi). In classical usage, it refers to personal letters or informal correspondence written on such slips, especially during the Han to Tang dynasties. The character 尺 denotes the standardized unit of length, while 牍 refers specifically to a flat, inscribed wooden board used for writing before paper became widespread.

Today, 尺牍 is a literary and historical term, rarely used in spoken modern Mandarin. It appears mainly in classical texts, academic discussions of early Chinese epistolary culture, or poetic allusions to elegant, handwritten letters. It carries connotations of sincerity, refinement, and scholarly intimacy — evoking an era when letter-writing required careful brushwork and thoughtful phrasing. While not part of daily conversation, recognizing 尺牍 helps learners appreciate how material culture shaped Chinese literary forms and communication traditions.