Triad of course means a trio. A triad is the basic 3 notes of a scale which make up a major or minor chord. Those 3 notes are the 1st, 3rd and 5th notes of the scale. Or, in sol-fa terms, the ‘do’, the ‘mi’ and the ‘so’. Here are the triad chords playable on a C/G Anglo.

C Major – C + E + G 

D major – D + F# + A

E major – E + G# + B

F Major – F + A  + C 

G major –G + B + D

A Major – A + C# + E

B major – B + D# + F#

D minor – D + F + A

E minor – E + G + B

F# minor – F# + A + C#

G minor – G + Bb + D

A Minor – A + C + E

B Minor – B + D + F#

5TH’s AND 7th’s  –  These are also chords you’ll use, particularly the 5th’s.  A 5th chord is just the triad minus the middle note. So, for example: C 5th ( which is written btw as C5) consists of ‘C’ + ‘G’.   The 5th chord is useful because it only requires 2 fingers, and it conveys a great dramatic, droney feel ideal for folk music. If you’re like me you’ll use 5th’s much more frequently than a full triad.

You ‘ll also notice that since the middle note of the triad is omitted, the 5th chord works both as a major or minor. So,  for example, a D5 can double as either a D major or a D minor.

7th’s ?   This means the triad with the addition of the flattened 7th of the scale ( a flattened ‘ti’ if you’re thinking in sol-fa,

Here are a couple of examples:

D7  is made up of  D + F# + A + C natural

A minor 7 is made up of  A + C + E + G natural

Generally you won’t be playing a full 4-note voicing of a 7th chord ( too awkward, particularly at speed). More often a 5th with the 7th. Like these:

C5/7  is made up of  D + A + C natural

G5/7 is made up of  G + D + F  natural.