What does preprocessor mean?
A preprocessor is a program that prepares data for another program or processing stage. It typically runs first: it may expand macros, substitute values, strip comments, normalize text, or convert one representation into another before the main application or compiler receives the input. In technical writing, “preprocessor” usually means a software tool rather than a separate machine, although the word can also refer more generally to a preliminary processing component. Its name reflects the sequence of work: pre- means “before,” while processor comes from process and ultimately from Latin procedere, “to go forward.” The term is especially common in programming, where source code is often altered by a preprocessor before compilation. Outside computing, it is relatively uncommon and tends to sound technical or institutional, as in a workflow that includes a preprocessor stage. It should not be confused with a processor, which carries out the principal computation, or with a postprocessor, which operates after that stage.
nounA computer program that prepares or transforms input before passing it to another program or processing stage.
- A computer program that performs preliminary transformations on data, source code, or text before another program or processing stage receives it.
"The C preprocessor expands macros before the compiler processes the source code."
"The C preprocessor expands macros before the compiler sees the source code."
"Run the text through a preprocessor to normalize whitespace and remove comments."
The word is countable and is pluralized with the suffix -s when referring to multiple preprocessing programs or components.
"The project includes separate preprocessors for text and image data."
It is the backstage crew for code: transforming the input before the main performance begins.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does preprocessor come from?
Preprocessor is a modern English compound formed from the Latin prefix pre-, meaning “before,” and processor, a device or program that carries out processing. Processor derives from process, which ultimately comes from Latin procedere, meaning “to go forward.” Related words such as proceed and procedure belong to the same Latin root family.
Related word forms
How preprocessor is actually used
This is primarily a technical computing term, especially common in discussions of compilers, text processing, and data pipelines. It can sound institutional when used outside computing to describe an initial stage in a workflow.
Easily confused with preprocessor
A preprocessor prepares input for another program or stage, whereas a processor performs the principal computing work.
A preprocessor acts before the main processing stage, while a postprocessor acts after it.