Approximation error is a common concept in mathematics and engineering that refers to the difference between an exact value and its approximate representation in a calculation or measurement. There are various synonyms for approximation error, depending on the context and the field of study. Some examples include: estimation error, rounding error, truncation error, numerical error, inaccuracies, deviations, uncertainties, imprecisions, and tolerances. Each one of these terms may imply a slightly different meaning or degree of precision, but they all refer to the idea that any approximation or measurement is subject to some level of error or uncertainty, which is important to account for in practical applications and scientific analysis.