Default setting
Most guitarists are familiar with the default setting of EADGBE. The default setting is the most commonly used in most guitar types. The interval between strings used in the default setting can be maintained while changing the pitch. By setting each string down an equal number of steps, the same chord and scale pattern can be used, but a lower key is used. The same open chord pattern for playing a song in A minor can be used to play the same song in G-minus if the strings are all set one step. A capo placed over the fretboards can raise the key in the same way.
Loose tuning
Locked settings lower the pitch of the six-string relative to the other strings. The most common drop tuning is Drop-D, which is DADGBE. These settings are mostly used by rock, metal and classical guitarists. These settings are usually used to play key D songs, with the open lower D string as a bass note for guitar parts. Some guitarists will also tune the strings as many steps from the Drop-D setting to play in lower settings.
Open Tunings
An open tuning is any tuning that forms a chord. This allows a guitarist to strum all six strings of the guitar unprotected and produce a useful chord. Open moods are usually main or smaller chords, but a more complex chord can be used. Open G (DGDGBD) is the most common version of this tuning. Slide players often use this setting because they have to form chords directly over a single fret due to the shape of the image. Keith Richards of the Rolling Stones is known for his use of Open G tuning. Keith Richards often uses chord changes that are physically impossible to perform by default. This setting allows the first chord to be formed with the index finger blocking a fret. This leaves the other three fingers free to make quick chord changes.
Instrument tunings
Instrument tuning mimics the interval pattern of another string instrument. These settings make it easier for a guitarist to play parts reminiscent of these instruments. For example, a six-string violin setting would consist of FCGDAE. These settings can be one octave higher or lower than the original instrument. The open strings of the guitar in a violin tuning would be lower than a violin because the guitar is a much larger instrument.
Regular interval settings
The default setting of a guitar has the interval between most adjacent strings as a perfect fourth. The interval between strings 3 (G) and 2 (B) is a large third. One method of alternative guitar adjustment is to use a regular interval for all strings. This can be any interval except unison or octave, which would make all the strings the same note. A guitar with a perfect fourth regular interval setting would be set to EADGCF.
Other settings
All combinations of six notes can be a guitar mood. There are tunings that do not meet the requirements for the other guitar tuning types. An example of this would be drone tuning, with all strings on the same note (DDDDDD). The twenty-four is another example, with guitar tuned DADDAD. This setting does not qualify as an open setting because it has only two different notes. Open chord setting requires the open strings to form a chord, which requires at least three different notes. The default setting for a six-string guitar is EADGBE, but many songs require different settings. Different guitar tunings allow the guitarist to play different types of chord progressions and riffs more easily. Songs that use these settings may not be practical or playable by default.
Source:danspela.com