sus2 and sus4 Chords

Forming Other Chords

Major dominant ninth with suspended fourth, found on the V degree of the scale. (Fifth is omitted)
Major dominant ninth with suspended fourth, found on the V degree of the scale. (Fifth is omitted). By Hyacinth at the English language Wikipedia, CC BY-SA 3.0, Link

I'm sure you've seen the word "sus" on music sheets and tabs. Sus is an abbreviation for "suspended", it refers to chords that don't follow the common triad pattern, whether major or minor triads, of 1 (root)+ 3 + 5. There are two commonly used types of suspended chords:

sus4 - A sus4 chord replaces the 1+3+5 pattern with 1+4+5, meaning the third note is replaced by the fourth. For example, the tab says you need to play a Dsus4 chord, instead of playing D+F#+A (=1+3+5) you raise the middle note or the third note by a half step.

So a Dsus4 chord is D+G+A (=1+4+5). Here are some commonly used sus4 chords for guitar.

sus2 - The sus2 chord follows the pattern 1 (root) + 2 + 5, so if in a sus4 chord you play the root, fourth and fifth notes, for a sus2 chord you play the root, second anf fifth notes. In other words, from a sus4 chord you lower the middle note three half steps. For example, a Dsus2 chord is D+E+A. Here are some commonly used sus2 chords for guitar.