macro Short for macroinstruction. An instruction in a programming language (almost always but not necessarily assembly language) that is replaced by a sequence of instructions prior to assembly or compiling. A macroassembler permits the user to define macros, specifying the macroinstruction form, its arguments, and a replacement text (otherwise called the body of the macro), and then allows macroinstructions to be interspersed among the assembly code. On encountering a macro the assembler replaces it by the macro body, substituting the parameters provided in the places marked in the macro body. The macro thus provides a mechanism for inserting a particular body of text at various places in a program (and is thus the same thing as an open subroutine, though this nomenclature is obsolete).

A macroprocessor provides similar facilities, though not in combination with an assembler. It accepts macro definitions and then reads arbitrary text in which macro calls (i.e. instances of a macro name) can occur. Text is copied to the output until a macro name is encountered: when this happens the arguments (parameters) are found and the macro call is replaced by the macro body in the output stream, with appropriate substitution of the parameters.

mac·ro / ˈmakrō/ • n. (pl. -ros) 1. (also macro instruction) Comput. a single instruction that expands automatically into a set of instructions to perform a particular task.2. Photog. short for macro lens.• adj. 1. large-scale; overall: the analysis of social events at the macro level. Often contrasted with micro.2. Photog. relating to or used in macrophotography.