Mansplaining is a portmanteau of the words man and explaining, defined as "to explain something to someone, typically a man to woman, in a manner regarded as condescending or patronizing." Lily Rothman of The Atlantic defines it as "explaining without regard to the fact that the explainee knows more than the explainer, often done by a man to a woman," and author and essayist Rebecca Solnit ascribes the phenomenon to a combination of "overconfidence and cluelessness.

Mansplaining covers a heterogeneous mix of mannerisms in which a speaker's reduced respect for the stance of a listener, or a person being discussed, appears to have little reason behind it other than the speaker's assumption that the listener or subject, being female, does not have the same capacity to understand as a man. It also covers situations in which it appears a person is using a conversation primarily for the purpose of self-aggrandizement — holding forth to a female listener, presumed to be less capable, in order to appear knowledgeable by comparison.