Definition: The word "code" is a generic term that loosely describes “the instructions that a computer follows when it's received”. In some instances the word describes software. In other circumstances it could mean encryption, the act of programming or being to describe malware. The term invariably refers to commands that can be given to a computer to read and execute. Malicious instructions (code) can be embedded into a computer or network to cause damage and diminish productivity.
Its Relevance: A computer must receive instructions to accomplish work. Literally, unless directives are received, a computer would sit for a hundred years (barring a power or hardware failure) and await a legitimate instruction from a user. Infrastructure owners must know what commands are being executed within the system from an information assurance standpoint. The main issue is that bad instructions or code must be eliminated from an information system. Programs of questionable origin and malicious intent have been discovered, for example, in the electrical grid.