In some languages, including C++, a macro is a piece of text that undergoes text substitution through expansion (translation) by the preprocessor before compiling.

A macro is a rule or pattern that specifies how a certain input sequence (often a sequence of characters) should be mapped to an output sequence (also often a sequence of characters) according to a defined procedure.

The term originated with macro-assemblers, where the idea is to make a sequence of computing instructions available to the programmer as a single statement, making programming less tedious and less prone to errors. Macro-instructions can eliminate some of the repetitiveness of programming, and also simplify the writing, reading and understanding of the program, because much of the program's complexity can be hidden.