Standard tuning defines the string pitches as E, A, D, G, B, and E, from lowest (low E2) to highest (high E4). Standard tuning is used by most guitarists, and frequently used tunings can be understood as variations on standard tuning. “Nonstandard” tunings are also called “alternative” or “alternate”. Some tunings are used for particular songs by professional musicians, and may be called after the song's title. There are hundreds of such tunings, which are often minor variants of established tunings. Communities of guitarists who share a musical tradition often use the same or similar tunings.