A rng has an abelian group under addition, an associative multiplication, and the distributive property; a multiplicative identity element is not required. Every ring under this wiki's unital convention is a rng. A nonunital ring may happen to have an identity: the terminology removes an axiom rather than imposing the absence of an identity. For example, the even integers with their usual operations have no multiplicative identity.
In algebra, particularly in the context of ring theory, the term "rng" (pronounced "ring") is an abbreviation that refers to a mathematical structure that is similar to a ring but does not necessarily require the existence of a multiplicative identity (i.e., an element that acts as 1 in multiplication).
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