A triad is a group of three notes. These notes are stacked in thirds. Since there are 2 types of third Interval, the major and minor, we can create the following groups.
Starting from the Root Note, we can move up 3 semitones (minor third) or 4 semitones (major third), to the Third then move up another major or minor third (3 or 4 semitones). The Fifth can then be 6 (diminished 5th), 7 (perfect fifth) or 8 (augmented fifth) semitones above the Root.
Contain a root, major third and perfect fifth interval
Contain a root, minor third and perfect fifth interval
Contain a root, minor third and diminished fifth interval
Contain a root, major third and augmented fifth interval