What is a letter?

Letters: This is the writing tool of the ancients. Before the invention of paper, bamboo or silk was used to make pages with long handles for writing notes, expressing feelings and transmitting information. Therefore, there have been many titles such as ruler element, ruler letter, ruler letter, ruler carp, ruler note, ruler letter, ruler book and so on, among which ruler letter is the earliest and most, so it has become synonymous with letters.