1. Any system of communication in which arbitrary groups of symbols represent units of plain text of varying length. Codes may be used for brevity or for security;
2. A cryptosystem in which the cryptographic equivalents (usually called "code groups"), typically consisting of letters or digits (or both) in otherwise meaningless combinations, are substituted for plain text elements which are primarily words, phrases, or sentences. (JP 1-02).
Source: Terms & Definitions of Interest for DoD Counterintelligence Professionals, Office of the National Counterintelligence, https://www.dni.gov/files/NCSC/documents/ci/CI_Glossary.pdf
3. Synonym for program or software versus to create or modify software.
Source: Information Technology Terminology, U.S. Election Assistance Commission, https://www.eac.gov/documents/2017/09/21/information-technology-terminology-security