在数学上，超现实数系统是一种连续统，其中含有实数以及无穷量，即无穷大（小）量，其绝对值大（小）于任何正实数。超现实数与实数有许多共同性质，包括其全序关系「≤」以及通常的算术运算（加减乘除）；也因此，它们构成了有序域。在严格的集合论意义下，超现实数是可能出现的有序域中最大的；其他的有序域，如有理数域、实数域、有理函数域、列维-奇维塔域（Levi-Civita field）、上超实数域和超实数域等，全都是超现实数域的子域。超现实数域也包含可达到的、在集合论里构造过的所有超限序数。

超现实数是由约翰·何顿·康威（John Horton Conway）所定义和构造的。这个名称早在1974年便已由高德纳（Donald Knuth）在他的书《研究之美》中就被引进了。《研究之美》是一部中短篇数学小说，而值得一提的是，这种把新的数学概念在一部小说中提出来的情形是非常少有的。在这部由对话体写成的著作里，高德纳造了「surreal number」一词，用来指称康威起初只叫做「number」（数）的这个新概念。康威乐于采用新的名称，后来在他1976年的著作《论数字与博弈》（On Numbers and Games）中就描述了超现实数的概念并使用它来进行了一些博弈分析。

In mathematics, the surreal number system is an arithmetic continuum containing the real numbers as well as infinite and infinitesimal numbers, respectively larger or smaller in absolute value than any positive real number. The surreals share many properties with the reals, including a total order ≤ and the usual arithmetic operations (addition, subtraction, multiplication, and division); as such, they form an ordered field. (Strictly speaking, the surreals are not a set, but a proper class.) If formulated in Von Neumann–Bernays–Gödel set theory, the surreal numbers are the largest possible ordered field; all other ordered fields, such as the rationals, the reals, the rational functions, the Levi-Civita field, the superreal numbers, and the hyperreal numbers, can be realized as subfields of the surreals. It has also been shown (in Von Neumann–Bernays–Gödel set theory) that the maximal class hyperreal field is isomorphic to the maximal class surreal field; in theories without the axiom of global choice, this need not be the case, and in such theories it is not necessarily true that the surreals are the largest ordered field. The surreals also contain all transfinite ordinal numbers; the arithmetic on them is given by the natural operations.