Banjo guitar is a term often applied to six-string banjos tuned like standard six-string guitars (E2-A2-D3-G3-B3-E4). Six-string banjos were first introduced in the late 19th century. Less widespread than its 4- and 5-string brethren, it was reintroduced in the latter part of the twentieth century with the modern guitar-like tuning.
The six-string "banjo guitar" should not be confused with the six-string Bluegrass banjo (played by Sonny Osborne and others), which retains re-entrant banjo tuning and a high-pitched drone string, simply adding a low G string to the five string banjo, nor with the zither banjo, a similar instrument from the late 19th/early 20th century, which was made in both five- and six-string models.