What are tunings?

Some articles on tunings, tuning:

Lap Steel Ukulele - Tunings
... The lap steel ukulele may be tuned to the standard ukulele tuning, or to an open tuning. ...
Leonard Kwan - Pioneer/Teacher
... In his youth, techniques, tunings, and even some songs were not freely exchanged but considered family secrets--one learned from family members and did not share with outsiders ... Kwan was the first player to publish the tunings he used on a recording, on the sleeve notes to The Old Way, which also included a transcription of the new version of "ʻOphihi ... Kwan's compositions and arrangements in a range of tunings, in standard notation and tablature, with performance notes and photographs of correct left-hand ...
Augmented Tuning - Instruments - Guitar
... Major-thirds (M3) tunings are unconventional open tunings, in which the open strings form an augmented triad in M3 tunings, the augmented fifth replaces the perfect fifth of the major triad of conventional ... Consequently M3 tunings are also called (open) augmented-fifth tunings (in French "La guitare #5, majeure quinte augmentée") ...
Tenor Guitar - Tuning
... normally tuned in fifths (usually CGDA, similar to the tenor banjo or the viola) although other tunings are possible, such as "guitar tuning", "Chicago tuning," or baritone ukulele ... be tuned like a soprano/concert/tenor ukulele, using various versions of GCEA tuning ... The normal CGDA tuning is very "open" and it gives the instrument unusual voicings from both open and closed chords ...
Augmented Tuning
... An augmented tuning is a tuning system for musical instruments that is associated with augmented triads, that is a root note, a major third, and an augmented fifth ... Augmented tunings are used for stringed instruments, especially guitars, and for wind instruments ... For guitars, augmented tunings are called major thirds tunings ...