# impure

/ˌɪmˈpjʊɹ/ (US) · /ɪmpjˈɔː/ (UK) · CEFR C1 · Adjective

Source: https://englishreference.com/word/impure
Updated: 2026-05-18

## Definition

containing something bad or unwanted. In programming, it means a value or data that is not in the correct format or is missing.

For teachers: containing an undesirable or incorrect component. In a programming context, it describes a value that fails to meet a specific type or validation constraint.

## Examples

- The function returns an impure value if the input is wrong.
- The system checks for impure data before it processes the transaction to prevent errors.
- In functional programming, an impure function is one that produces different results for the same input or has side effects that alter the program's state.

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From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.