quasireal

Quasireal is a term used in different disciplines with no single universally accepted definition. In mathematical writing, it is typically an informal descriptor rather than a formal object, applied to quantities or entities that are real-like but do not strictly belong to the real numbers.

In nonstandard analysis, some authors describe certain hyperreal numbers as quasireal when they are finite and infinitely close to a real number. In this usage, a quasireal would be a member of the hyperreal line that maps to a real under the standard part function. However, this usage is not universal, and other sources simply call such objects “finite hyperreals.”

In computational and applied contexts, quasireal has been used to refer to numerical values known only to a fixed precision, i.e., real-valued quantities approximated within a tolerance. In measurement and modeling, the term often conveys the idea of real-valued estimates subject to rounding, noise, or model error.

In philosophy or foundations of mathematics, quasireal can appear in discussions of realism about numbers or in debates about what counts as a “real” value within an extended theory of arithmetic.

Because quasireal is not a standardized term, readers should consult the specific source for how the authors define it in that context. See also real numbers, hyperreal numbers, nonstandard analysis, and numerical approximation.