Bosniaks, often referred to as Bosnian Muslims, are a South Slavic ethnic group and nation native to Bosnia and Herzegovina. They share a common ancestry, culture, history and the Bosnian language; and traditionally and predominantly adhere to Sunni Islam. The Bosniaks constitute significant native communities in Serbia, Montenegro, Croatia and Kosovo as well. Largely due to displacement stemming from the Bosnian War and Genocide in the 1990s they also form a significant diaspora with several Bosniak communities across Europe, the Americas and Oceania.

Bosniaks are typically characterized by their historic ties to the Bosnian historical region, adherence to Islam since the 15th and 16th centuries, and the Bosnian language. Bosniaks have also frequently been denoted Bosnian Muslims in the Anglosphere mainly owing to this having been the primary verbiage used in the media coverage of the Bosnian War during the 1990s. However, this term is today considered problematic for several reasons when intended as an ethnic descriptor rather than a religious one. Bosniaks may also often simply be referred to as Bosnians, though this term is understood to denote all inhabitants of Bosnia and Herzegovina (regardless of ethnic identity) or apply to citizens of the country.

According to the Bosniak entry in the Oxford English Dictionary, the first preserved use of "Bosniak" in English was by English diplomat and historian Paul Rycaut in 1680 as Bosnack, cognate with post-classical Latin Bosniacus (1682 or earlier), French Bosniaque (1695 or earlier) or German Bosniak (1737 or earlier). The modern spelling is contained in the 1836 Penny Cyclopaedia V. 231/1: "The inhabitants of Bosnia are composed of Bosniaks, a race of Sclavonian origin". In the Slavic languages, -ak is a common suffix appended to words to create a masculine noun, for instance also found in the ethnonym of Poles (Polak) and Slovaks (Slovák). As such, "Bosniak" is etymologically equivalent to its non-ethnic counterpart "Bosnian" (which entered English around the same time via the Middle French, Bosnien): a native of Bosnia.

From the perspective of Bosniaks, bosanstvo (Bosnianhood) and bošnjaštvo (Bosniakhood) are closely and mutually interconnected, as Bosniaks connect their identity with Bosnia and Herzegovina.

The earliest attestation to a Bosnian ethnonym emerged with the historical term "Bošnjanin" (Latin: Bosniensis) which denoted the people of the medieval Bosnian Kingdom. By the 15th century, the suffix -(n)in had been replaced by -ak to create the current form Bošnjak (Bosniak), first attested in the diplomacy of Bosnian king Tvrtko II who in 1440 dispatched a delegation (Apparatu virisque insignis) to the Polish king of Hungary, Władysław Warneńczyk (1440–1444), asserting a common Slavic ancestry and language between the Bosniak and Pole. The Miroslav Krleža Lexicographical Institute thus defines Bosniak as "the name for the subjects of the Bosnian rulers in the pre-Ottoman era, subjects of the Sultans during the Ottoman era, and the current name for the most numerous of the three constituent peoples in Bosnia and Herzegovina. Bosniak, as well as the older term Bošnjanin (in Lat. Bosnensis), is originally a name defining the inhabitants of the medieval Bosnian state".

Linguists have most commonly proposed the toponym Bosnia to be derived from the eponymous river Bosna; widely believed to be a pre-Slavic hydronym in origin and possibly mentioned for the first time during the 1st century AD by Roman historian Marcus Velleius Paterculus as Bathinus flumen.

Linguist Petar Skok expressed an opinion that the chronological transformation of this hydronym from the Roman times to its final Slavicization occurred in the following order; *Bassanus> *Bassenus> *Bassinus> *Bosina> Bosьna> Bosna.

According to the English medievalist William Miller in the work Essays on the Latin Orient (1921), the Slavic settlers in Bosnia "adapted the Latin designation [...] Basante, to their own idiom by calling the stream Bosna and themselves Bosniaks [...]".