The diatonic scale or major scale refers to the set class (unordered collection of notes) with twelve transpositions of the white keys. This scale is common in many cultures and across styles of music. The seven modes of the diatonic scale include the Ionian or Major mode (Do-Re-Mi-Fa-So-La-Ti-Do), the Natural Minor mode, and more.
The scale is maximally even, symmetric and related to transpositions of itself by single-semitone voice leadings. In fact, each transposition of the diatonic (major) scale has six scales that are each a semitone voice-leading step away: two other diatonic (major) scales; two acoustic (melodic minor) scales; and one harmonic major and one harmonic minor scale.
See A Diatonic Puzzle for more about what makes the diatonic scale unique, and Staff Notation for more on how the diatonic scale is deeply embedded into standard staff notation. See Diatonic Modes & Chords for more about how the modes and chords fall out of the notes of the major scale.