Levi-Civita field

Etymology
Named after.

Noun

 * 1)  A non-Archimedean ordered field whose every member $$a$$ can be constructed as a formal series of the form $$a = \sum_{q\in\mathbb{Q}} a_q\varepsilon^q ,$$ where $$a_q$$ are real numbers, $$\mathbb{Q}$$ is the set of rational numbers, and $$\varepsilon$$ is to be interpreted as a fixed positive infinitesimal.