Ahir is an Indian caste. The term can be used synonymously with Yadav, as the latter term refers to Ahirs who have identified as Yadavs. The major divisions of Ahirs are: Yaduvanshi, Nandvanshi, and Gwalvanshi.

Ahir is a Prakrit form of the Sanskrit word abhira (fearless),^{[citation needed]} The Indologist F. Max Müller stated in 1886 that the Abhira are the modern Ahir.

Various theories exist regarding the origin of the Ahirs.

Sir William Wilson Hunter proposes that the word Ahir derives from the Sanskrit Ahi (snake) and that snake worship, compounded by other cultural facts, suggests a Scythic origin.^{[citation needed]} However, J. C. Nesfield refutes it by saying that snake worship is not peculiar to scythics but a common practice all over India, and he also argues that it is absurd to derive Ahir from ahi, a Sanskrit word, when the original name of the community is Abhira, and Ahir its Prakrit corruption. One study^{[citation needed]} in Deccan Ahirs have found out existence of totemistic septs, which is regarded as a sure sign of being non-Kshatriya, seconded by existence of a sect called Romabans, which is the regular corruption of word romak, frequently found in Sanskrit works on astronomy, and identified by Prof. Weber to be the town Alexandria in Egypt, from where the science of astronomy was cultivated and from whom people of India borrowed the concepts of astronomy. It is argued that foreign hordes from Romak might have settled in India, and incorporated into Ahirs.