In the nomenclature of musical terms side A and side B (called the A-side and B-side) refer to the two sides 7-inch disc gramophone, on which singles have been recorded from the 50s They refer to the types of tracks appearing on each side: the main song was on the side A and side B (which is also called "Flipside" ") contained less popular song (often absent even longplayach contractor). Szelakowe earliest 10-inch panels were unilateral. Bilateral disc containing one song on each side, were introduced in Europe by Columbia Records and the end of 191