In telecommunication, a line code is a code chosen for use within a communications system for transmission purposes.

Note 1: A line code may differ from the code generated at a user terminal, and thus may require translation.

Note 2: A line code may, for example, reflect a requirement of the transmission medium, e.g. , optical fiber versus shielded twisted pair.

Source: from Federal Standard 1037C and from MIL-STD-188