符是秦汉时期广泛使用的一种凭证。根据形制和功能的不同，可以将其分为以铜虎符、竹使符为代表的中央用符和基层所用竹木符两类，前者主要来源于节，后者则与券相关。秦汉时期，二者的尺寸、使用方式和功能迥异，发展趋势也各不相同，中央用符是国家权力的象征，一直延续至后代；基层用符形式灵活、使用广泛，但随着政务形式的变化、简纸交替过程的发生，逐渐走向衰亡。此外，魏晋以降，“符”还成为一种下行文书的称谓，其含义为“命令”“约束”，与作为凭证的符没有关系。

The Fu was a widely used credential in the Qin and Han dynasties. Based on their functions and shapes, they can be divided into two categories: the central Fu represented by the copper tiger Fu and the bamboo Fu used at the grassroots level. The former mainly originated from metal talismans, while the latter was related to bamboo and wooden vouchers.During the Qin and Han periods, these two types of Fu differed significantly in size, usage, and functions, and their development trends also varied. The central Fu was a symbol of state power, and although it underwent changes, it continued to exist in later generations. On the other hand, the grassroots Fu was more flexible in form and widely used, but it gradually declined as administrative practices changed and paper replaced bamboo and wooden writing materials.Furthermore, from the Wei and Jin dynasties onward, the term "Fu" evolved to refer to a type of downward official document, meaning "command" or "constraint", which had no relation to the Fu used as a credential.