Discography is the study and cataloging of published sound recordings, often by specified artists or within identified musical genres. The exact information included varies depending on the type and scope of the discography, but a discography entry for a specific recording will often list such details as the names of the artists involved, the time and place of the recording, the title of the piece performed, release dates, chart positions, and sales figures. A discography can also refer to the recordings catalogue of an individual artist, group, or orchestra. This is distinct from a sessionography, which is a catalogue of recording sessions, rather than a catalogue of the records, in whatever medium, that are made from those recordings. The two are sometimes confused, especially in jazz, as specific release dates for jazz records are often difficult to ascertain, and session dates are substituted as a means of organizing an artist's catalogue. Another, more recent, definition of discography refers to a collection of musical recordings by a performer or composer, considered as a body of work. For instance, all studio albums by a performer could collectively be considered their discography. The term "discography" was popularized in the 1930s by collectors of jazz records. Jazz fans did research and self-published discographies about when jazz records were made and what musicians were on the records, as record companies did not commonly include that information on or with the records at that time. Two early jazz discographies were Rhythm on Record by Hilton Schleman and Hot Discography by Charles Delaunay. A compilation of a performer's piano rolls is called a "rollography."