A dashiki is a loose shirt from West Africa. They are collar-less, pullover, short-sleeved shirts. They are traditionally quite loose and large, often falling to mid-thigh. They are stereotypically brightly colored cotton prints with elaborate embroidery or bright patterns, which nearly always includes a false placket.
What exactly qualifies as a dashiki is a bit up in the air. The garment in its current form was introduced in America as part of the Black Pride movement in the 1960s by Oba Ofuntola Oseijeman Adelabu Adefunmi. As such, it is fair to say that the dashiki as seen in America, and as described above, is the 'true' dashiki. However, the word comes from the Yoruba term danshiki, meaning a sleeveless tunic, and various related tunics have been present in West Africa for centuries. Today you can find many related tunics in Africa, including not only mirrors of the 'American' dashiki, but also versions with long sleeves, true plackets, longer skirts, hems flared with gussets, and any number of other modifications.
The full dashiki suit will traditionally consist of a dashiki, a kufi cap, and sokoto trousers. However, the dashiki often appears in America as part of the hippie, slacker, and beach bum aesthetic, and is probably most often worn with jeans.
Dashiki is pronounced da-she-ki (IPA /də.ˈʃi.ki/).