The ethnonym Afghan (Pashto: افغان) has been used historically to refer to the Pashtuns. Since the second half of the twentieth century, the term "Afghan" evolved into a demonym for all residents of Afghanistan, including those outside of the Pashtun ethnicity.

The earliest mention of the name Afghan (Abgân) is by Shapur I of the Sassanid Empire during the 3rd century CE. In the 4th century, the word "Afghans/Afghana" (αβγανανο) was used in reference to a particular people as mentioned in the Bactrian documents.

"To Ormuzd Bunukan, from Bredag Watanan ... greetings and homage from ... the sotang (?) of Parpaz (under) the glorious Yabghu of Hephthal, the chief of the Afghans, the judge of Tukharistan and Gharchistan. Moreove, a letter [has come hither] from you, so I have heard how [you have] written to me concerning my health. I arrived in good health (and) afterwards (?) I heard that a message was sent thither to you (saying ) thus : ... look after the farming but the order was given to you thus. You should hand over the grain and then request it from the citizens store: I will not order, so ... I myself order and in respect of winter sends men thither to you then look after the farming. To Ormuzd Bunukan, Greetings."

— Bactrian documents, 4th century

"because [you] (pl.), the clan of the Afghans, said thus to me: ... And you should not have denied (?) the men of Rob [that] the Afghans took (away) the horses."

— Bactrian documents, 4th century, Sims-Williams 2007b, pp. 90-91.

"[To...]-bid the Afghan... Moreover, they are in [War]nu (?) because of the Afghans, so [you should] impose a penalty on Nat Kharagan ... ... Lord of Warnu with ... ... ...the Afghan... ..."

— Bactrian documents, 4th century, Sims-Williams 2007b, pp. 90-91.