Jian 箋 is a type of commentary.
The character originally referred to bamboo or wooden slips (jian du 簡牘) used for writing before the invention of paper during the Han period 漢 (206 BCE-220 CE). The word in the common sense was first used for commentaries on the Confucian Classic Shijing "Book of Songs" (Maoshi jian 毛詩箋 by Zheng Xuan 鄭玄, 127-200). The fragmentarily surviving character dictionary Zilin 字林 by Lü Shen 吕忱 (4th cent.) explains that the word jian meant "to express [a meaning]" (biao 表) or "to recognize, to clarify" (shi 識). Yu Jaxi 余嘉锡 (1884-1955) writes in his Shuce zhidu bukao 書冊制度補考 (ch. Jian 箋) that Zheng Xuan used bamboo slips for his commentaries on the Shijing, perhaps one slip per annotation. Other words for commentaries are jianshi 箋釋, jianzhu 箋注, jianshu 箋疏 or jianzhuan 箋傳. The word jianshu 箋述 means "to write, to compile".
The character 箋, e.g. in the combination jianzou 箋奏/牋奏, is interchangeable with jian 牋, which refers to a kind of semi-public letter (shuzha 書札, xinzha 信札, jianshu 箋書/牋書, jianzha 箋札, jianjian 箋簡) or addresses (zouji 奏記, jianji 箋記, jianqi 箋啓/牋啓) presented to empresses, heir apparents, and princes, or functionaries of very high rank. Another meaning of 箋/牋 is writing paper of fine quality used to compile poems or to write letters (xinjian 信箋, huajian 花箋 or jinjian 錦箋).