A letter is an applied document that transmits information and exchanges thoughts and feelings to a specific object. "Xin" has the meaning of audio and news in ancient Chinese, such as "the anode is on the top, and the yin is on the bottom." (Yang Xiong: Xuan Jingying); In addition, "letter" also means that the words conveyed by the trustee are credible, whether it is the information sent by the trustee or the letter posted by the postman to convey information and exchange thoughts and feelings with a specific object. First, it has the ability to tell stories in words and express its thoughts and feelings; The second is to have corresponding writing tools; Third, someone passed it on. Writing letters to relatives and friends in person can not only convey your thoughts and feelings, but also give the trustee a sense of intimacy. With the continuous progress of science and technology, telephone, telegraph, mail tape, video tape, e-mail and other means of exchanging information have appeared one after another. It can be predicted that more and more people will use email in the future. With the development of society, the relationship between man and society is being reconstructed. In addition to the traditional usage, that is, official letters and private letters, a new development trend is the transactional letters sent to government agencies, enterprises and institutions, famous scholars and other individuals for personal needs. It is noteworthy that the use of such letters is increasing gradually. We call it a private document.
In addition, in ancient times, letters, as the main source of communication, not only conveyed the cultural exchanges between countries, but also conveyed people's thoughts and feelings (to their elders, lovers and friends in their hometown ...), and also played a profound role in reporting peace.