Major triad
A major triad is a triad comprising a root, major third, and perfect fifth.
In just intonation
The 5-limit major triad is 4:5:6, found on the I (1⁄1), IV (4⁄3), and V (3⁄2) of Ptolemy's intense diatonic scale (Zarlino).
The 3-limit major triad is 64:81:96, found on the I, IV, and V of the Pythagorean diatonic scale.