Sus chords (which is short for suspended) replace the third of a chord with another scale degree. For example, a C major chord, C-E-G, becomes a Csus2 by replacing the third, E, with the second, D (to form C-D-G). Because the third determines the major or minor quality of a chord, sus chords are neither major or minor. This "incomplete" sound makes them very versatile.

For example...

D Major
e|-2-----------2----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

Dsus4
e|-3-----------3----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

D Major
e|-2-----------2----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

Dsus2
e|-0-----------0----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

This is one of my favorite chord sequences, D-Dsus4-D-Dsus2 played in Travis style arpeggio. I always find myself playing this every time I pick up an acoustic. Again, Dsus2 is a D chord with the third replaced by the second, and Dsus4 has the third replaced by the fourth. All three chords sound bright and major (to me, anyhow.) Now check out the next example.


D Minor
e|-1-----------1----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

Dsus4
e|-3-----------3----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

D Minor
e|-1-----------1----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

Dsus2
e|-0-----------0----|
B|-------3----------|
G|----2-----------2-|
D|-0--------0-------|
A|------------------|
E|------------------|

This is just like the other example, but with D minor replacing the D. With the one chord change, the whole progression sounds different. The sus chords now sound sad and minor, taking on the quality of the minor chord.

I love to use sus chords as a "pivot" between major and minor chords, or to finish a progression for that unresolved sound.