In this section we'll go over the four types of triads and their chord symbols.
Triads consist of three notes which are the first, third and fifth note of a scale. You can also think of them as a couple third intervals stacked on each other.
Let's start with the most common triad, a major triad. The chord symbol for a major triad is just the capital letter of the name of the chord, i.e. C is the symbol for C major triad. Sometimes you will also see the symbol Cmaj as well. This triad has the root note (the note that is also the name of the chord), the major third and a perfect fifth. It consists of a minor third stacked on a major third (in a C major triad, C to E is a major third, and E to G is a minor third.) Here's all twelve major triads:
The next most common triad is a minor triad. The chord symbol for minor triads is a dash, lower case m, or 'min' and is written as C-, Cm, or Cmin. It has the root note, the minor third and the fifth. It consists of a major third stacked on top of a minor third (in a C minor triad, C to Eb is a minor third, and Eb to G is a major third). The only difference from a major triad is that the third (the middle note) is down a half step.
The next triad isn't as common, the diminished triad. The chord symbol for diminished triads is a circle or dim. For example, C diminished triad is written as Cº or Cdim. It has the root note, a minor third and a diminished fifth. It consists of two minor thirds stacked on each other. The difference from a major triad is that the top two notes are lowered a half step.
The final triad is also pretty rare, the augmented triad. The chord symbol for an augmented triad is a plus sign or aug. So C augmented triad is written as C+ or Caug. It has the root note, a major third and an augmented fifth. It consists of two major thirds stacked on each other. The difference from a major triad is that the top note (the fifth) is raised a half step.
Here's the four types of C triads: