A telegraph code is a character encoding used to transmit information through telegraphy machines. The most famous such code is Morse code (Wikipedia page [1]).

More information on the Wikipedia page [2]

The Chinese Telegraph Code, Chinese Telegraphic Code, or Chinese Commercial Code (simplified Chinese: 中文电码; traditional Chinese: 中文電碼; pinyin: Zhōngwén diànmǎ or simplified Chinese: 中文电报码; traditional Chinese: 中文電報碼; pinyin: Zhōngwén diànbàomǎ) is a four-digit decimal code (character encoding) for electrically telegraphing messages written with Chinese characters.

More information on the Wikipedia page [3]

The Railway Codes website page [4]

An article on telegraph codes is here [5].

See also Commercial code (communications)