"Open tuning" refers to a guitar tuned so that strumming the open strings produces a chord, typically a major chord. The base chord consists of at least 3 notes and may include all the strings or a subset. The tuning is named for the open chord, Open D, open G, and open A are popular tunings. All similar chords in the chromatic scale can then be played by barring a single fret. Open tunings are common in blues music and folk music, and they are used in the playing of slide and bottleneck guitars. Many musicians use open tunings when playing slide guitar.