What is leading tone in a major scale?

Generally, the leading note is the seventh tonal degree of the diatonic scale leading up to the tonic. For example, in the C major scale (white keys on a piano, starting on C), the leading note is the note B; and the leading note chord uses the notes B, D, and F: a diminished triad. In Music Theory, the leading note triad is symbolized by the Roman numeral vii°.