in computer hardware, a word mark or flag is a bit in each memory location on some variable word length computers (e.g., ibm 1401, 1410, 1620) used to mark the end of a word. sometimes the actual bit used as a word mark on a given machine is not called "word mark", but has a different name (e.g., "flag" on the ibm 1620, because on this machine it is multipurpose).